I'm not sure what the problem is, is this intended? I just need to edit the title. I hover my mouse over my post and I don't see any "edit" options or any kind of option, actually. The same problem occurred to me a while back, but it's getting annoying now.
This is a flaw with the way polls (and blogs that are posted to the forum) work. Basically, the '1st' post that is linked to the title isn't actually the top post, but rather the 2nd one down..and that one's hidden by default. For blogs you can of course still edit the 1st post content via the blog on your profile itself, whereas the 1st post content on a poll is essentially set in stone. The only way I've found to edit the hidden 2nd post is URL manipulation - basically adding /edit onto the thread URL manually. This will (or at least used to) make the hidden post visible in the thread when done successfully as well, though it can easily be re-hidden via deletion of just the post.
It's a known issue, but I have no idea when it'll be fixed, it's probably an underlying problem with the way they're made and as such likely isn't as simple to fix as it may seem.