Steps to Reproduce

1. Open the GUI of a command block.
2. Enter execute as @s, then copy-paste as @s repeatedly enough to make the text field start scrolling horizontally. (Any other long command should work, but this is the one I used to test.)
3. Move the cursor back to an instance of as @s roughly in the middle of the text field.

Expected Behavior

The autocomplete window should show at the cursor position.

Actual Behavior

The autocomplete window appears all the way to the right of the text field (see attached screenshot).