Spacing with arrow keys "jumps" out of focus

I’m having an issue similar to this: Spacing Keyboard Shortcuts 'Dropping out'
Often when I edit LSB then switch to RSB with the tabulation key, focus is lost after one press. So I can add 1 unit (or 10 if I also press Shift), after which the focus is not in the spacing field. If I had a selection in the glyph, it even edits the outlines! So quite a nasty bug because it can mess the design without me noticing.
I’m never getting the error sound mentionned in the other post.
I’m not able to reproduce the bug constantly, but it happens constantly without me doing anything special (using different settings or plugin). Sometimes it does, sometimes not.

I should specify that I’m in edit mode, Select (V) tool, and click the LSB number to edit spacing.

I can’t reproduce this. Can you post a screen recording?