Android back button navigation pop does not trigger onWillChangeTab

As the title says: When a tab is changed from an Android back button press, the callback onWillChangeTab is not being triggered.

I already have a back button handler from where I could call that manually, but I would need access to the tab id in that case.

Is the observed behaviour a bug?
Is there a way to get the relevant tab id from within my custom back button handler so that I could implement a workaround?