I just tested this, and it won't post the poll if I do not post accompanying comments (in the regular area where one posts, like where I am writing now) - if I leave that blank and only do a poll it won't work. But when I wrote some stuff there (in this case testingtestingtesting), the poll posted. Some just write a little text about your poll in the comments area.
I think the deal is because the poll is not a post/thread in itself - it's an attachment. So if you write nothing, it won't psot, the same way you can't start a thread with a blank message. The page will reload itself when you hit submit until you put something in that comment area.
HTH!
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~ dc
"Anyone who lives within their means suffers from a lack of imagination" - Oscar Wilde