Apper currently ships with a downstream hack (apper-0.9.2-style.patch) that
makes it refuse to use the systemwide Qt widget style. This was done to
workaround a harmless, purely cosmetic glitch (bug #1209017). But it causes
a much worse cosmetic glitch: the application looks just completely off.
Just compare the big progress bar on a stock Fedora 24 installation (where
Oxygen is not available, and thus Cleanlooks is used) with a Breeze progress
bar. It just looks completely wrong.
Please see the discussion at:
I was asked to bring this to the mailing list, so I am doing that hereby.
IMHO, native KDE applications must not be disguising themselves as GTK+
applications when running under Plasma.