As I mentioned in a previous post, the only thing that resolved the issue for our company was going to the local apple store talking to the genius bar. They swapped the problematic hardware out, and the new hardware is working fine.
I'm not sure what caused our problem. The only thing that I can come up with is that maybe there is some bad sectors of memory in the phone, and when the mail app tries to use that memory it causes a problem with mail.
We were able to rule out connectivity issues. We tested this by starting a sync and stepping into an elevator where there is no signal. The sync failed, but it didn't cause the mail to reload. We tested running the phone on a couple of combinations of cellular and wifi also, but again failed to reproduce the error.
We also tried sending a few thousand emails to a user to make a large number of changes to the mailbox and couldn't reproduce the issue.
Ben