I never had a sync problem with any of my exports in CS5.
It's not a bug that I'm aware of. More likely a local issue on your system.
I also never have had any synch issues with WMV and H.264 MP4 exports (or anything else) in any of the CS versions.
I also have never noticed any posts regarding this as an issue either ...so not sure who ..
...all of us who paid good money for CS5 have had to live with this issue for more than a year
I found a bug with WMV sync with 23.976 CBR encodes in CS6, but it was fixed with the 6.0.1 update. I never had any issues prior to CS6.
I upgraded to CS6 and, sure enough, problem's gone.