We got an example of the user which has last edit (proper contribution) few months ago, but there are entries in the FlaggedRevs review log which indicate the user is reviewing changes.
When doing "get IP addresses" or "get edits" the message is shown:
No matches found. Last edit was on 5 January 2014 at XX:YY.
Either FlaggedRevs is not logging to CheckUser or CU query is broken. Need to recreate the case on the test wiki.
Filing under "Extension:CheckUser" for now unless proven innocent.