laughinghan/mathquill — comment on commit 6462e02431dfb541ab5c9a17eea9f2678dd8900e
File:  line 0
By pesasa:

Here "randomly" seems to depend on odd or even number of keystrokes.
Example:
1) Write in mathquill box (in mathmode) `123456`.
2) Hold shift key and tap left arrow three times to select `456`.
3) Press ctrl-x to cut -> no effect.
4) Press ctrl-x again -> `456` is cut.
5) Press ctrl-v to paste.
6) Hold shift key and tap left arrow four times to select `3456`.
7) Press ctrl-x to cut -> works.

If the selection is done with mouse, the cut, copy, paste works.

I think the problem with selecting text inside math mode with keyboard is connected with this.