Userpage of disabled user says: "User does not belong to any projects."
Some active project lists given user as the project member.
Assuming it has something to do with disabling of user, since I haven't noticed similar inconsistency with any active user (not saying that it doesn't exist thoug).
OTOH another disabled user shows being member of some projects where he is listed.
The former user (inconsistent) has been disabled at about Dec2015/Jan2016, the latter has been disabled around May2015 - hope that helps a bit to find relevant versions and changes between them.
Can't reproduce since not having necessary rights nor have versions from that time available to test.