I mentioned something ..
I have an article with pollfield .. i made a new node and added many polls to it.. when people vote one poll . all polls are set to close.. after deep looking . i saw that this is happening only to polls that are set to Unlimited time..
so if a poll has a limited time, no problem
if a poll has an unlimited time, all polls will close that are set to unlimited after one poll gets Voted in that node.