CT: Assertion failed: cannot start a drag when already userControlled

[zepumph]

No description provided.

[jessegreenberg]

I started seeing this with ?fuzzBoard during phetsims/scenery#1570. But I think it may be an issue with how Masses are reset. Here is what I am seeing:

1. MassView.focusablePath has a focus listener that calls mass.start. This sets userControlledProperty to true. The path receives focus.
2. Somehow (maybe the ResetAllButton) calls Mass.reset and sets the userControlledProperty to false.
3. Then, the MassView.focusablePath gets a blur event. There is a blur event listener that tries to call mass.endDrag. Since userControlledProperty.value has been reset, this causes the assertion.

If the order of operations with KeyboardDragListener seems wrong, let me know and I would be happy to keep looking.

[zepumph]

Ahh goodness, sorry that I made you investigate. This is totally on my side. I'm not really sure how this code path is occurring, but I'm thinking it is just because of how keyboard fuzzing is applying many keyboard events in the same frame. I added grace above and I cannot reproduce now. Closing