User is able to set the Section Time to a value that's beyond the current length of the montage. This breaks the animation and the user can see issues in the UI as well (such as the timeline marker actually moving off the bar).
The new time location is accepted. When the animation plays, it's stop animation at final frame but the timeline will continue.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-47001 in the post.