v18 - Directly close TVGuide with "Back" when Fullscreen Video1

Hi,

i'd like to adapt the Estuary Mod2 Skin in the following way (i believe with Standard Estuary it's the same behaviour):

When i open the TVGuide with the "Guide" key on my remote (which is mapped to "E") while LiveTV is running, and then Close it with "Back", i get into the main menu, livetv is running in the Background, and I have to press "Back" again to see Fullscreen LiveTV again. So I'd like this to change in a way that in case LiveTV is running the TVGuide closes immediately when pressing "Back".

I've tried to add the tag 

<previouswindow>fullscreenvideo</previouswindow>

in the <window> Definition of the XML file. This works fine if really a Fullscreen Video (like livetv) is displayed. But if i call the tvguide from the main menu without a running Video in the Background and close it again, then Kodi stucks, since there is no "fullscreenvideo" So i've tried to add a condition to the previouswindow tag:

<previouswindow condition="Player.HasVideo">fullscreenvideo</previouswindow>

or 

<previouswindow condition="Pvr.IsPlayingTv">fullscreenvideo</previouswindow>

but this did not work, same behaviour as without the condition. 

Any hint what i'm doing wrong?

PS: I've also tried to use an Action in the <onunload> tag of the window (a 2nd "Back" or "Close"), but this lead to weired effects (some Kind of a "closing Loop")

Cheers Louis