Mmm, hard to see what we can do here without patching something quite low level.
Ideally we would want it to remain in CARP maintenance until the states have syncd. That would probably need to be selectable though as some people will not be syncing states.
We could probably force the Primary to boot into maintenance mode at every boot requiring manual intervention to failback. It would still failback automatically if the secondary went off-line entirely. Would that be in any way practical for you?
Steve