I might have a fix for this. I ran into the issue a week or two ago and wrote up some CSS that appears to fix it. I’d like to do a little more testing for bad side effects before I post it.
I am pretty sure something changed in core Discourse recently that led to the problem since I definitely remember a time when it wasn’t happening. Unfortunately, this type of thing happens with add-ons. The Discourse team can’t be expected to test every change against every customization that’s out there.
Anyway, I’ll try to get the CSS posted this weekend if a solution isn’t posted in the mean time.