[KaliS]

i was having this issue as well after initially installing wm6.5 and like everyone else, it was an annoying pain. i read a possible fix on this forum and it has worked for me. i'll state it again and hopefully it will also work for others. i hope i'm not posting something that has been mentioned many times already in this thread.

this is what i did, really simple:
1) back up data on phone (activesync for me does it)
2) reinstall wm6.5
3) turn off phone after installation is completed and first reboot
4) conducted a hard reset (press "Send" & "End" keys, plus the "Power" button on top of the phone, then let your phone fully reboot).

this worked fine for me and i haven't had a single issue since.