I have a Blackberry 8800 and it behaves very strange:
It deletes nearly every single Message on the device during an unexplored time cycle (I hope you understand my english)
I don't have any option activated for automatic deletion so I can't explain it.
It's strange because 3-5 messages stay on the device with unspecified date.
I never had some problems with my 8700 and I love the blackberry plattform, so what's that on my 8800?
It now happened 3-4 times during 3-4 months and I'm VERY unhappy with this failure!
I bought an old 8700 as Backup and as soon as it arrives I will send in my Blackberry for service.