The bug

When you get a list of possible entries to auto-complete (e.g. possible entity/block/item id) and you move cursor into "unintended" position (e.g. put it between coordinates) and then press Tab, you'll get one of the entries of the list inserted, even though it is not supposed to be there

Steps to reproduce

1. Tab-complete (or write) /setblock, so it has all coordinates filled
2. (not necessary) Write incomplete id which has multiple ways to be completed (e.g. purpur can be completed with _block, _pillar and so on)
3. Press tab a few times to complete the block id, so that suggestions for other ids are displayed in chat
4. Move the cursor with mouse to the coordinates in the /setblock command and press tab again

→ Minecraft still auto-completes the block id instead of the coordinate