KWin currently ignores the _NET_WM_FULLSCREEN_MONITORS property on windows. This property is used to control over which monitors an applications wants to be displayed. Generally this contains either a single monitor, or all of them.
KWin claims to support this feature though as it has _NET_WM_FULLSCREEN_MONITORS in _NET_SUPPORTED.
Tested on Fedora 27, but we've gotten reports from other distributions as well. Our bug entry:
There is a "Video Wall" script that sort-of works as a workaround. However it also ignores _NET_WM_FULLSCREEN_MONITORS and just assumes all monitors should be used, ignoring the application's settings.
What frameworks version are you using
Please tell your distribution to ship bug fixes in a timely manner.
*** This bug has been marked as a duplicate of bug 391960 ***
Hmm... Just to make sure I'm not misunderstanding things. The patch on bug 391960 looks like it is touching client code? I'm seeing this problem with non-KDE applications. They're not even using Qt.
You are misunderstanding. Just because it says client doesn't mean it's code running in clients. Trust me, an update will fix it.
Awesome. Will wait until I get my hands on an updated system and retest.