I'm not sure about all of the places this bug exists for me, but I've found one example.

In the Forum Shop, whenever I buy something, I purchase two of it.

I've edited some screenshots to show what I mean :D

This does not happen when I use Microsoft Edge for some reason, but does happen on a clean install of Chrome.

AFAIK this bug happens with Bones as well, though I cannot check today anymore.

I figured out the method and everything, but I can't win when I select the same number twice due to the bug.

I've noticed this because the number of bones jumps from 27 all the way to 19 or so after my first turn.