Hi Ben.Driehuis,
To answer the question, “Is this change of behavior intended?” I’ve consulted the developers and received the following explanation:
"Yes, this is intentional. The reasoning behind this is that once a Montage has been stopped, it is no longer active and you cannot do anything to it anymore. You cannot change its position, play rate, section, etc. as you have stopped it and that’s not a reversible action.
Also, if you are pushing another montage on the same group, the previous one will be marked inactive and blend out. If you want to use any of the Montage API functions, it will reference the new active montage, and the other one is basically stopped, inactive, and going away."
I’m glad to hear you were able to come up with some work-arounds and hope this clarifies the reasoning behind the change in how the GetActiveMontageInstance works.