Try fixing #2107 by removing checkRep

src/static/js/ace2_inner.js

@@ -742,8 +742,8 @@ function Ace2Inner(){
     assem.append(o);
     Changeset.appendATextToAssembler(atext, assem);
     var newLen = oldLen + assem.getLengthChange();
-    var changeset = Changeset.checkRep(
-    Changeset.pack(oldLen, newLen, assem.toString(), atext.text.slice(0, -1)));
+    var changeset = Changeset.pack(oldLen, newLen, assem.toString(), atext.text.slice(0, -1));
+    // changeset = Changeset.checkRep(changeset)
     performDocumentApplyChangeset(changeset);
 
     performSelectionChange([0, rep.lines.atIndex(0).lineMarker], [0, rep.lines.atIndex(0).lineMarker]);
@@ -2333,7 +2333,7 @@ function Ace2Inner(){
       if(rep.selStart[1] == rep.selEnd[1] && rep.selStart[1] == rep.lines.atIndex(n).text.length){
         return false; // If we're at the end of a line we treat it as having no formatting
       }
-      if(rep.selStart[1] == 0 && rep.selEnd[1] == 0){ 
+      if(rep.selStart[1] == 0 && rep.selEnd[1] == 0){
         rep.selEnd[1] == 1;
       }
       if(rep.selEnd[1] == -1){
@@ -3818,7 +3818,7 @@ function Ace2Inner(){
             // top.console.log(caretOffsetTop, viewport.top, caretOffsetTopBottom, viewport.bottom);
             var caretIsNotVisible = (caretOffsetTop < viewport.top || caretOffsetTopBottom >= viewport.bottom); // Is the Caret Visible to the user?
             // Expect some weird behavior caretOffsetTopBottom is greater than viewport.bottom on a keypress down
-            var offsetTopSamePlace = caretOffsetTop == viewport.top; // sometimes moving key left & up leaves the caret at the same point as the viewport.top, technically the caret is visible but it's not fully visible so we should move to it 
+            var offsetTopSamePlace = caretOffsetTop == viewport.top; // sometimes moving key left & up leaves the caret at the same point as the viewport.top, technically the caret is visible but it's not fully visible so we should move to it
             if(offsetTopSamePlace && (evt.which == 37 || evt.which == 38)){
                 var newY = caretOffsetTop;
                 setScrollY(newY);