AbuseFilter can, through the 'block autopromote' setting, revoke the autoconfirmed status of any user that triggers a filter. That status can be restored through Special:AbuseFilter/tools, however that operation is not logged anywhere.
For transparency, I feel this should be logged in the AbuseLog. Something like:
- 00:00, 1 January 2013: Administrator (talk | contribs | block) restored the autoconfirmed status to Example (talk | contribs | block)