Also I think they are letting you vote sooner than an hour...at least it seems that way to me. I know I have voted more often than this, but I am not sure why it let me.
One reason it may not recognize you: the poll software uses your IP address to figure out if you have voted in the last hour. Most of the time, your IP address is randomly assigned each time you log on, unless you're amogn the relatively small minority who have a static IP address.
So, if you disconnect and then reconnect, you have another IP address and the poll software may not recognize you from your prior visit.