Steps to reproduce :

- import the Mecanim Example Project
- create a new Animation Controller
- create a blend tree and assign two motions
- add a model to the scene
- add the newly created blend tree to the Animator Component
- press play and notice the error regarding the parameter and the model is not moving (as expected)
- in play mode disable and enable the Apply Root Motion checkbox and notice that the model is playing the animation
- exit playmode
- enter playmode again and notice that the model is broken and sometimes the console is spammed with errors

*Note :
Video and screenshot attached.
This is not a regression, reproducible on 5.0a10 as well.