UI not updating even though the model differs

[Timo T]

Bug Report

Steps to Reproduce:

1. Checkout https://github.com/Azzurite/fn-fx-update-bug/
2. Run -main
3. Click on "Goto Settings"

Expected Result:

Expect "MainPane content!" to change to "Settings content!"

Actual Result:

"MainPane content!" stays displayed

Environment:

Windows 10 x64, JDK 1.8.0_191 (also does not work under OpenJDK 11.0.1 with the other dependency)

Additional Context:

Happened in a more complex program of mine. I can get the change to work by wrapping one of the GridPanes with a StackPane, apparently that manages to "trick" the diff algorithm into thinking something actually changed.

You can see that in the example repository in the workaround branch.

I managed to trace the bug to somewhere in the diff-component fn in fn-fx.diff, but didn't manage to understand that fn.