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.
- Place a command block
- Open the full command text box
- type out at least 1 full line of text of any type, (use more lines for more pronounced effect)
- Move the cursor along that line and try to add text to it
- 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.