Concurrency problem?

Hi,
We experienced a problem with this module: we asked users to change their password at their next login, but some of them were continuously being asked to change their password. After some investigations, I saw that, for these users, $user->force_password change == 0, but their uid was in the force_password_change_pending_login_users variable.

Could it be possible that force_password_change_pending_login_users suffers from a concurrency problem, when two users get and set this variable at (almost) the same time?

Maybe a SQL table would be more appropriate in this case?

Patrick