Inconsistent browser history with turbo frame

I notice a behavior which may surprise users with turbo frame. Whenever user nagivates within the scope turbo frame, all he sees is the same url even the underlining url is different. When he hit “back” button in browser, he jump back to the previous non-turbo-frame page. It is an expected behavior so far.

But when the user nagivates out of the turbo frame and then hit “back” button, he sees the last turbo frame page instead of the first one. That might be surprising because the url is the first turbo frame, not the last one.

Here is a diagram between the url the user see and the actual url:

I hope this explanation is clear. I do not suggest which behavior is better, but it would be better to be consistent.