ModelItem(FlowSwitch) PropertyChanged Event In Custom Activity Designer

Question

I wrote a custom activity with activity designer
I handled ModelItem(FlowSwitch<string>) PropertyChanged event then try to delete or swicth case to Default
The PropertyChanged just trigger "Defalut", not trigger "Cases". Why?

And PropertyChanged trigger by "Default", i try to get "Cases" property the value is Old??

Any idea?

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Microsoft Taiwan