Just this Layer.reinterpolate() bit errors in this:
Traceback (most recent call last):
File "<macro panel>", line 18
File "GlyphsApp/GlyphsApp/__init__.py", line 9736, in Layer_replaceLayerWithInterpolation
objc.error: NSInternalInconsistencyException - enableUndoRegistration: NSUndoManager 0x12c6314d0 is in invalid state, enableUndoRegistration may only be invoked with matching call to disableUndoRegistration
G 3507