User A invites a resource with maximum bookings set to 1 to an event at a given date and time.
User B invites later the same resource with a recurring event at the same time. The event of user B does starts on a date before the event of user A, but one of the recurring parts hits the event of user A.

The event of user B is happily accepted even on the clashing event date without any warning!

Because of this the resource is overbooked on this date.
Both users can look at their events and both will see that this ressource has accepted their event invitation.

Only if user B tries to modify the clashing occurency she will get the "Maximum number of simultaneous bookings (1) reached for ...." Error, which prevents her to store her change.

Expected behaviour:
User B gets the overbooked Error when trying to store the recurring event with a hint on which occurency it happens, preventing the overbooking.