It’s hard to tell really without a link as sounds very like this could be due to your theme. If you can provide a link that would be great. Alternatively, could you try the default BuddyPress theme and see if it happens there? I understand on a live community this may not be possible.
If it’s not theme related it could be some plugin / something adding CSS / scripting and clashing. I’d therefore you look at if you can striping back plugins to try and find the culprit. It does sound this is the less likely thing though and it’s something in your theme.
What’s funny, is that the theme developers were blaming buddypress. Since it was my first buddypress installation, I checked everywhere and then decided to post some comments on about 10 different buddypress sites…..none did as I mentioned..so I dropped the theme and made my own bp theme from a non-bp theme and everything is good now. Sorry for such a late reply.