Breaking clips wont allow you to change its length afterwards as there are no animaiton data, only the last freeze frame

Steps to reproduce:

1. New project
2. Import any character
3. Add animation
4. Split the Motion clip in half
5. Try to extend the first half to its original length

Result: there are no more data after the cut

Workaround: You have to use the resize tool and resize the clip where the cut should be. That will allow you to change its lenght afterwards but the work is very tedious

Suggestion: Redesign the Motion clip editing in a way that you can cut it, resize it from both sides and not loose clip's data (similar to how Premiere handles video clips)