Incorrect primitive position when skin property set to null

If skin property of a primitive node is set to some valid Skin node and then set back to null, the primitive node position is incorrect.
To reproduce:
1) Run the attached example:
The Model node position changes every 500ms, but the mesh position is not affected, as it is skinned to some joints located outside of the Model hierarchy.
2) Press the gray button at the top-left corner of the window
The skin settings are reset and the skin property is set to null. It is expected that the mesh position should be affected by the timer, which shifts it by 0.1 every 500ms, but it doesn't happen.
To prove that the problem somewhere in handling of the Skin node set it to null in the code and restart the program. Now the mesh position is affected by the timer.

It should work even if Skin node is not set to null, as if initially it is set to valid Skin node, but the geometry is not skinned, it works as expected.