How to reproduce:
1. Open the attached project
2. Select panda sprite and open Sprite Editor
3. Select one of the pandas and switch to Bone Editor
4. Select Create Bone and start adding bone (and change its name)
5. Create few bones on panda and click Escape
6. Select Create Free Bone and add few bones
7. Undo all stelps with CMD+Z
8. Repeat 4-7 steps (just don't change the name)
Result: after clicking Undo twice bones apper in the corner of sprite sheet.
After clicking undo third time one should get ArgumentOutOfRange error