Montage gets 10 more frames than animation sequence

I created a montage with a 50 frames animation sequence, the new montage got 60 frames, why?

I have problems with montages too. When I update the animations, the montage doesn’t get updated. Could that be your case? I have to remove and re-add the animation to the montage.
And I have more problems. The montage notifies also stop working in this case. I have to move them in order to make them work again.