Press T in Full Screen Mode

In my opinion it's not a bug, but rather a feature.

The fact that toolbar is not shown in fullscreen mode doesn't mean you shouldn't be able to enable or disable it.

I mean you may think that pressing T in fullscreen mode does nothing, but actually it does.

It switches toolbar state as in the normal mode, the effect is just visible only when you exit fullscreen mode.

Yeah, formally that is a bug, but I doubt very much that it will be high on the list of bugs to fix... It's the kind of bug that makes me think of this well known joke:

Patient: "Doctor, if I press here, it hurts."

Doctor: "Do not press there."

Exactly. That's my point. There shouldn't be a pop up saying anything at all about showing the toolbar because it can't be shown. It's a bug. Try it yourself and you'll see. 

In the full screen mode the toolbar can't be shown.

Or what you mean exactly?