Unfortunately, that is the truth.
Whenever multiple choice is allowed, people are able to choose an option, then go back and choose another one, if they can't decide what they take on something is, or if the poll creator desired to allow multiple voting. It can be abused, however, as any person possessing a login name is able to vote for the same option over and over, not making it any fair.
Now, the most horrible side of these things, *THE* GLITCH. It's a story. I had problems with my internet connection once, and my vote didn't count. I kept clicking the button we're supposed to hit when we want to make the opinion count, thinking the site "didn't let me through" for a weird reason. Then I got the pop up thingy approving my 'vote'. Well, I was surprisied to find out that I just ruined a poll, and there was not just a single vote, but a few hundred ones, as I was "clicking through" for a couple of minutes to the rhythm of the song I was listening to.
Before I get called a young offender, I would like to point out that this is hardly a normal gitch. I just repeated my action by memory on one of the older polls on site, and it seems that it still works. And I wouldn't be surprised that people are taking advantage of it as we speak, just like they have always had. Basically, to conclude all I've said, you don't need much time to ruin a poll. It's not ever neccessary to sit at home for hours clicking the button and waiting for approval, and then repeating this process in hope of being the poll ruining King. It takes a minute to change the results of a poll completely. This isn't a question to be discussed, and this isn't anything else but a problem. You can't deny it, as I have tested it myself, much more important is what is possible to do in this situation.
I am no computer genius, but I sugger either:
a) removing the feature.
b) not removing the feature, but when the poll is set forcing the person to choose the option he likes and ONLY THEN press the vote button, and not allowing him to be able to vote again.
I also suppose it should be noted that it is useless to think people will be credible enough, as sometimes even the more faithful to the site do horrible things to bring their favourites up, or just out of total boredoom.