video restarts when I skip ahead

every time I skip ahead on a video, the shuttle moves forward but the video loads from the beginning. This behavior happens in Firefox, Safari and Chrome. I have tried a clean install and the behavior is still the same.

I am using Shockwave Flash 11.5.502.110

I am on a Mac

OSX 10.6.8

Intel Core Duo

4GB of RAM

latest versions of Firefox, Safari and Chrome (but this problem has been happening for the past 5 months)