On a newly installed and fully updated Mountain Lion system, I see the following problem:
After a few minutes of using Mail.app (or even just letting it sit in the dock), the inbox becomes empty. More precisely, the inbox of an Exchange mail account becomes empty. If I let the program sit in the dock, I receive new mail notifications, but I can't read the messages because the inbox looks empty.
Restarting Mail.app is a temporary fix, but the problem will come back in a few minutes.
Has anyone seen this problem? Are there any solutions? I did not do anything special which could have caused this and my inbox is small (less than 100 MB---I did read that this can happen when the inbox is too large)