I believe this is an issue with RU5. I had similar issues where the client defs would go out of date some 2 weeks before finally updating themselves automatically. Stopping and starting the SMC service sometimes caused the systme to update as well, but the one thing that always worked was live update. Does running LU update the definitions? Obviously that isn't the fix, but I would be curious if that at least updates the defs.
If it is the same issue, I can confirm that it is resolved post RU5.