Seems i had the permission set incorrectly to allow you to create polls where you could revote. This should be fixed for all forums now. If by any chance I scrwed something else up let me know, e.g something doesn't work that worked before, something dissappeared etc. The permission settings are quite extensive and completely customizable but it also comes at the price of being quite complicated.
Think I have a pretty good handle on them now, this is actually one frequent complint about phpbb from admins and has been for years.