Cursor jumping out of position while typing in line with multicursor

[segphault]

If you type inside of a line that contains another user's cursor, your own cursor will jump after every key press. You can observe this on the QuillJS site example page: http://quilljs.com/examples/

Steps to reproduce:

1. In the basic example box, click right before the "S" in "Shadows" in the first line of the last paragraph
2. In the full example box, click right before the "M" in "Mordor" in the same line
3. Begin typing

Results: the cursor will immediately jump to the very beginning of the line after the first character appears.

Some observations that might help you isolate the issue...

If you start typing after the position of the other cursor (e.g. at the end of "Shadows") the cursor will jump to the very end of the line instead of the beginning. This behavior doesn't appear to occur when the other cursor is at the very beginning or very end of the line, however.

Also, if you do this in a line that has some formatted text in it, the cursor will move forward or backward to the formatted text instead of the beginning or end of the line if the formatted text is first.

[jhchen]

Reports like these are how bugs get fixed. Thanks!