I haven't had a chance to check this out yet (in fact, I haven't even tested it on my board to see if it's doing the same thing).  However, I did stumble across a topic in Mod Troubleshooting that seems to somewhat relate.  It's a solution to multidel and polls.  It seems to describe your problem almost exactly.  The issue at hand within that topic seems to be nested tables, so the solution in this case would be to find out if there are any nested tables, and figure out a way to get rid of them.

Okie dokie - after testing it out on my boards, it seems that everything works just fine there.  So, it must be something specific that you have installed on your boards.  We'll have to do a little more research specifically into what you've got in your files.