Hit Bump, power windows go down

[Nick 986]

Had a weird one happen today. As I was driving out to the beach, I drove over a small bump across the highway. It was an area that had some patchwork paving done at some point. It was a small bump nonetheless but whan I drove over it I heard a click and my windows went down the same distance as if I was putting the convertible top up or down. I tried to put the windows back up and they would not move. I could put them down but they would only go back up to that point and no further. I opened the handle on the convertible top and closed it back up and the windows worked fine. This happened to me once before about three years ago and today was only the second time it happened. Obviously it is extremely intermittent but I am just curious as to what would cause this to happen. Thanks again in advance for your replies.