SOLVED (kind of) - Menubar looks 'strange'

My menu bar looks like this, i.e. ‘Help’ is displayed at the very left:

However, pressing the ALT key or using the mouse to select something in the menu bar, it turns into what I would expect it to be:

I tried starting a clean copy (alternative configuration), and it seemed to work fine for a short while, then started behaving the same.

Slightly annoying, but I can work my way around it most of the time.

EDIT: issue has disappeared, I have no clue whatsoever what I’ve done to fix it. Sorry.