Like many of you I applied SP2 a while back and promptly added  a few classes back to the sms_def.mof, however I had enable the Cal tracking too and it is enabled within the configuration.mof.

Today I realized that it was disable (default setting) because both the smsdef.mof and configuration.mof are over written as part of applying the service pack. Therefore if you did have it enable and you applied the SP for ConfigMgr, remember to re-enable it.