Mail Application Deletes messages iPhone

Sometimes I accidentally delete an email. However, I then usually go into the trash and move the message back to my inbox (all done within the native mail application). However the two most recent times this has occured, two emails (one important) have been permanently deleted. It was as if I had deleted them from the trash (which would permanently delete them). At first I figured I may have accidentally hit the delete button instead, but the second time I am positive that I hit the correct move to inbox button. Does anyone know why this is happening?
Iphone 3G iOS 4