Browser object does not detect fullscreen if set outside of C3?

I have fullscreen working fine. But now I also wanted to be able to set it directly from the framing webpage by requesting fullscreen for the iframe that contains the C3 game. Again, it works fine, but my toggle fullscreen sprite/button inside the game does not adjust. It relies on condition Browser object Is fullscreen to set its animation frame.

So, what gives? Does set fullScreen in Construct apply to another element than the iframe or does Is fullscreen check an internal variable?