A couple of my users had the same issue, both of their Tours are running 18.104.22.168. No reoccurrences reported after they performed a hard reset. None of my Tour users on either 22.214.171.124 or 126.96.36.199 have reported the problem yet, knock on wood.
BES 4.1.6 MR8 (Win2003 SP2)
Exchange 2003 SP2