Thanks! That's pretty bizarre, but I think I have a clue what might be wrong, I probably just wasn't persistent enough to reproduce it.
Viewing post in Trans Neuronica Prelude comments
I don't know if it will help, but I tried on Edge on the same laptop, got the same behaviour. Tried it on a Macbook in Chrome, couldn't reproduce (although I got a similar behaviour in a weird case that might be related if I expand the hud then quickly click below it).
The video that Nogodsnomaster posted looks like the problem I had, except I hit fewer "unseen buttons" (for lack of a better term right now), so I won't clutter up your inbox with a second one (unless it'll help). And if it matters (although probably not, since it sounds like you have an idea) - Windows 11, 22H2 22621.1555, Chrome 112.0.5615.50 here. (and in case the size of the game area might have an impact, 4K monitor, since that's just one non-obvious thing I can think of that's different between my two laptops where I tested it)