I have an application which crashes SA when a field is changed. I don't know that I am able to recreate the scenario so I've attached an application that causes SA to crash.
The application is slimmed down to a tree store and a model. The store includes static data to be displayed in a tree grid. Making a change to the model field 'Builtin', such as changing the field type, causes SA to crash. At least for me. Perhaps your mileage will vary.
After much trial and error the error can be eliminated by editing the static data in the store's 'root' property.
I'm providing this post as a heads-up in case it lets you understand why SA crashes.