diff --git a/src/static/js/ace2_inner.js b/src/static/js/ace2_inner.js
index f8a8d847b..def7b0900 100644
--- a/src/static/js/ace2_inner.js
+++ b/src/static/js/ace2_inner.js
@@ -1455,16 +1455,6 @@ function Ace2Inner(){
     var selection = getSelection();
     p.end();
 
-    function topLevel(n)
-    {
-      if ((!n) || n == root) return null;
-      while (n.parentNode != root)
-      {
-        n = n.parentNode;
-      }
-      return n;
-    }
-
     if (selection)
     {
       var node1 = topLevel(selection.startPoint.node);
@@ -1486,12 +1476,8 @@ function Ace2Inner(){
       var nds = root.getElementsByTagName("style");
       for (var i = 0; i < nds.length; i++)
       {
-        var n = nds[i];
-        while (n.parentNode && n.parentNode != root)
-        {
-          n = n.parentNode;
-        }
-        if (n.parentNode == root)
+        var n = topLevel(nds[i]);
+        if (n && n.parentNode == root)
         {
           observeChangesAroundNode(n);
         }
@@ -5034,6 +5020,23 @@ function Ace2Inner(){
       if(e.target.a || e.target.localName === "a"){
         e.preventDefault();
       }
+
+      // Bug fix: when user drags some content and drop it far from its origin, we
+      // need to merge the changes into a single changeset. So mark origin with <style>,
+      // in order to make content be observed by incorporateUserChanges() (see
+      // observeSuspiciousNodes() for more info)
+      var selection = getSelection();
+      if (selection){
+        var firstLineSelected = topLevel(selection.startPoint.node);
+        var lastLineSelected  = topLevel(selection.endPoint.node);
+
+        var lineBeforeSelection = firstLineSelected.previousSibling;
+        var lineAfterSelection  = lastLineSelected.nextSibling;
+
+        var neighbor = lineBeforeSelection || lineAfterSelection;
+        neighbor.appendChild(document.createElement('style'));
+      }
+
       // Call drop hook
       hooks.callAll('aceDrop', {
         editorInfo: editorInfo,
@@ -5051,6 +5054,16 @@ function Ace2Inner(){
     }
   }
 
+  function topLevel(n)
+  {
+    if ((!n) || n == root) return null;
+    while (n.parentNode != root)
+    {
+      n = n.parentNode;
+    }
+    return n;
+  }
+
   function handleIEOuterClick(evt)
   {
     if ((evt.target.tagName || '').toLowerCase() != "html")
diff --git a/tests/frontend/specs/drag_and_drop.js b/tests/frontend/specs/drag_and_drop.js
new file mode 100644
index 000000000..bcec0bd29
--- /dev/null
+++ b/tests/frontend/specs/drag_and_drop.js
@@ -0,0 +1,160 @@
+// WARNING: drag and drop is only simulated on these tests, so manual testing might also be necessary
+describe('drag and drop', function() {
+  before(function(done) {
+    helper.newPad(function() {
+      createScriptWithSeveralLines(done);
+    });
+    this.timeout(60000);
+  });
+
+  context('when user drags part of one line and drops it far form its original place', function() {
+    before(function(done) {
+      selectPartOfSourceLine();
+      dragSelectedTextAndDropItIntoMiddleOfLine(TARGET_LINE);
+
+      // make sure DnD was correctly simulated
+      helper.waitFor(function() {
+        var $targetLine = getLine(TARGET_LINE);
+        var sourceWasMovedToTarget = $targetLine.text() === 'Target line [line 1]';
+        return sourceWasMovedToTarget;
+      }).done(done);
+    });
+
+    context('and user triggers UNDO', function() {
+      before(function() {
+        var $undoButton = helper.padChrome$(".buttonicon-undo");
+        $undoButton.click();
+      });
+
+      it('moves text back to its original place', function(done) {
+        // test text was removed from drop target
+        var $targetLine = getLine(TARGET_LINE);
+        expect($targetLine.text()).to.be('Target line []');
+
+        // test text was added back to original place
+        var $firstSourceLine = getLine(FIRST_SOURCE_LINE);
+        var $lastSourceLine  = getLine(FIRST_SOURCE_LINE + 1);
+        expect($firstSourceLine.text()).to.be('Source line 1.');
+        expect($lastSourceLine.text()).to.be('Source line 2.');
+
+        done();
+      });
+    });
+  });
+
+  context('when user drags some lines far form its original place', function() {
+    before(function(done) {
+      selectMultipleSourceLines();
+      dragSelectedTextAndDropItIntoMiddleOfLine(TARGET_LINE);
+
+      // make sure DnD was correctly simulated
+      helper.waitFor(function() {
+        var $lineAfterTarget = getLine(TARGET_LINE + 1);
+        var sourceWasMovedToTarget = $lineAfterTarget.text() !== '...';
+        return sourceWasMovedToTarget;
+      }).done(done);
+    });
+
+    context('and user triggers UNDO', function() {
+      before(function() {
+        var $undoButton = helper.padChrome$(".buttonicon-undo");
+        $undoButton.click();
+      });
+
+      it('moves text back to its original place', function(done) {
+        // test text was removed from drop target
+        var $targetLine = getLine(TARGET_LINE);
+        expect($targetLine.text()).to.be('Target line []');
+
+        // test text was added back to original place
+        var $firstSourceLine = getLine(FIRST_SOURCE_LINE);
+        var $lastSourceLine  = getLine(FIRST_SOURCE_LINE + 1);
+        expect($firstSourceLine.text()).to.be('Source line 1.');
+        expect($lastSourceLine.text()).to.be('Source line 2.');
+
+        done();
+      });
+    });
+  });
+
+  /* ********************* Helper functions/constants ********************* */
+  var TARGET_LINE = 2;
+  var FIRST_SOURCE_LINE = 5;
+
+  var getLine = function(lineNumber) {
+    var $lines = helper.padInner$('div');
+    return $lines.slice(lineNumber, lineNumber + 1);
+  }
+
+  var createScriptWithSeveralLines = function(done) {
+    // create some lines to be used on the tests
+    var $firstLine = helper.padInner$('div').first();
+    $firstLine.html('...<br>...<br>Target line []<br>...<br>...<br>Source line 1.<br>Source line 2.<br>');
+
+    // wait for lines to be split
+    helper.waitFor(function(){
+      var $lastSourceLine = getLine(FIRST_SOURCE_LINE + 1);
+      return $lastSourceLine.text() === 'Source line 2.';
+    }).done(done);
+  }
+
+  var selectPartOfSourceLine = function() {
+    var $sourceLine = getLine(FIRST_SOURCE_LINE);
+
+    // select 'line 1' from 'Source line 1.'
+    var start = 'Source '.length;
+    var end = start + 'line 1'.length;
+    helper.selectLines($sourceLine, $sourceLine, start, end);
+  }
+  var selectMultipleSourceLines = function() {
+    var $firstSourceLine = getLine(FIRST_SOURCE_LINE);
+    var $lastSourceLine  = getLine(FIRST_SOURCE_LINE + 1);
+
+    helper.selectLines($firstSourceLine, $lastSourceLine);
+  }
+
+  var dragSelectedTextAndDropItIntoMiddleOfLine = function(targetLineNumber) {
+    // dragstart: start dragging content
+    triggerEvent('dragstart');
+
+    // drop: get HTML data from selected text
+    var draggedHtml = getHtmlFromSelectedText();
+    triggerEvent('drop');
+
+    // dragend: remove original content + insert HTML data into target
+    moveSelectionIntoTarget(draggedHtml, targetLineNumber);
+    triggerEvent('dragend');
+  }
+
+  var getHtmlFromSelectedText = function() {
+    var innerDocument = helper.padInner$.document;
+
+    var range = innerDocument.getSelection().getRangeAt(0);
+    var clonedSelection = range.cloneContents();
+    var span = innerDocument.createElement('span');
+    span.id = 'buffer';
+    span.appendChild(clonedSelection);
+    var draggedHtml = span.outerHTML;
+
+    return draggedHtml;
+  }
+
+  var triggerEvent = function(eventName) {
+    var event = helper.padInner$.Event(eventName);
+    helper.padInner$('#innerdocbody').trigger(event);
+  }
+
+  var moveSelectionIntoTarget = function(draggedHtml, targetLineNumber) {
+    var innerDocument = helper.padInner$.document;
+
+    // delete original content
+    innerDocument.execCommand('delete');
+
+    // set position to insert content on target line
+    var $target = getLine(targetLineNumber);
+    $target.sendkeys('{selectall}{rightarrow}{leftarrow}');
+
+    // insert content
+    innerDocument.execCommand('insertHTML', false, draggedHtml);
+  }
+});