Comment # 18 on bug 1100765 from Wolfgang Bauer

So we probably should reassign this bug report, or close it as upstream?

Btw, I think the reason why it works when using dbus-launch is that it uses its
own new DBus session bus then (created by dbus-launch), where the already
running kwin doesn't show up at all...
I suppose you would run into same problem if you do a sequence like this:
export `dbus-launch`
kwin5_x11 --replace
gimp

whereas it should work with:
export `dbus-launch`
gimp

Just guessing though, as I wrote I still have gimp 2.8 which doesn't seem to
have this issue. (maybe it doesn't have "KDE/kwin support code" yet...)