I'm not sure what the html includes, but we do not allow script and iframes (for obvious reasons . Maybe it has something to do with that?
I have a link in my signature to my Twitter feed, and people can then click the '+Follow' button. Asle has something similar, but then with a little Twitter icon.
Yes, the problem is probably with the script - especially if it tries to report back how many people already follow you.
I see this problem elsewhere as well, with the the Facebook "3 of your friends like this" or the Google+ graphics.