Reproduction steps:
1. Open the attached project "kitchen.zip";
2. Select Anima2D component of WeabooAnima2DTest;
3. Open up Animation tab;
4. Move bone around from handle (little black dot) twice;
5. Undo (Ctrl+Z) the actions;
6. Mem errors should now be visible in the console (SI console);

Expected results: bones should be in their original position immediately;
Actual results: this moving causes errors in the console and Unity hangs for a while.

Reproduced on: 5.6.0f3, 2017.1.0b1;
Not reproduced on: 5.5.0f3.