Only that there is a cache somewhere that insists on clearing itself regardless of whether cached mode has been turned off or not.... in other words, turning off caching prevents new files being sent to the cache, but for obvious reasons the cache still wants to complete it's task.
I don't know that, just a guess. Of course, some undiscovered virus could do something like that as well.
If you could discover the location of my imagined cache, you might clear it using safe mode or some such.
Just wild speculation from someone that doesn't use Outlook and has never used an exchange server. :P