No. is blocked, call monitor stays open
If a number is blocked in the fritzbox and the number is calling, the call monitor stays open.
This happens only for blocked numbers. 

Maybe because its kind of reverse in handling? It first disconnects the caller and then it shows incoming call.

09:53:14HOME Bridge FritzPlatform Callmonitor (group): Call disconnected with blocked
09:53:14HOME Bridge FritzPlatform Callmonitor (group): Incoming call from: blocked to private