The current behavior during maintenance is that a readonly view of the site is presented, and modification tools like voting, commenting, and retagging don't work. Great, very sensible.
The problem is that if you don't hover a few seconds to get the tooltip that says the action is disabled because of maintenance, the response to the click is very unhelpful. It actually tells you to log in, despite the fact that won't help, and even when you already are logged in. I suppose that's because some
CanVote function is returning false. CanVote is not a boolean though, there should be: True, GuestsCannotVote, ThisPostIsLocked, ThisPostIsDeleted, TheSiteIsReadonly, NoVotingPrivilege -- and only one of these should lead to a login prompt.
Because "readonly; therefore please login" is just invalid reasoning.
Please change the popup triggered by a click during readonly to highlight the in-maintenance status of the site, not prompt for login. I used voting on an answer to illustrate this, but it should be applied to all actions unavailable in readonly mode during maintenance.