I'm running Lion, connecting to an Exchange 2010 server. Sent messages are stored locally.
Once I've replied to a messages in my Inbox, the "replied" arrow appears to the left of the message, as normal. But when I click on the arrow to see the actual reply it fails roughly 50% of the time. By "fails" I mean that nothing comes up when I click. A message I sent minutes earlier/later can work just fine.
The reply WAS sent using Apple Mail (not my iPhone) and it IS in my sent mail folder. I have re-built my Spotlight index.