I have noticed this as well on mine. I have T-Mobile and using an 8320. I have had the same phone for 6 months no problem. 2 months ago it started, at first just once a week, then more often, now it happens daily, sometimes 2 or 3 times a day.
I also went back to my unlocked ATT 8310, same problem, then tried a T-Mobile 8120.
Now i have a co-worker using my unlocked ATT 8310 with NO problems. I am in the process of re-loading the newest official 4.5.xx.xxx off the T-Mobile website. Based on this happening to multimple devices, then not when other people use them, I have decided its either a T-Mobile, RIM or something glitchy on my account in the system causing this. I dont think its the physical device its self.
I am glad to see its happening to someone else.
Other steps i have tried. Re-Sending service books. Deleted all email accounts. Removed 3rd party apps. Used JL Cmdr to wipe the device and re-install the hand held software.
As we speak i am re-loading the hand held softare again with out any apps, and then send new service books.