Random port already forwarded/open?

[baldcast]

I am currently unable to forward ports and have pretty much stopped using utorrent as a result. However, yesterday I was using a port that I believed to be random as well as a dynamic IP address. It turned out that for some reason utorrent's checker indicated that this port was open. I was quite pleased and my speeds were very impressive. But today, the checker indicates that the same port is not open and as a consequence my speeds are weak. I have not changed any settings. What is this a result of? Could it be that this port is only open underneath the IP address I was using yesterday and today my dynamic IP changed and the port is no longer open? Are some ports just randomly open for no reason? If anyone can answer any of my questions or help me in any way, please post. Thanks in advance.