Lots of text makes the Cursor Inaccurate

The cursor within command blocks gets increasingly inaccurate the more test there is.

It seems to be linked with line count but this is just what it seems. I from here-on assume it is due to the line count.

Steps to Reproduce:

1. Place a command block
2. Open the full command text box
3. type out at least 1 full line of text of any type, (use more lines for more pronounced effect)
4. Move the cursor along that line and try to add text to it
5. Typing will be inaccurate to the cursor (behind) to the same amount of lines you have -1

The video shows the effect happening with 3 lines which makes the cursor 2 text places off from where the cursor is located.