I'm using archlinux. The plasma-desktop package used to co-install (in /opt/kf5) with KDE4. But the latest version (5.0.2) now installs to /usr, thus conflicts with kdebase-workspace 4.11. So I removed kdebase-workspace.

Then KDE4 apps (e.g. Dolphin) no longer use the widget style I set earlier (qtcurve), and fall back to the default Plastik style.

I tried to change the widgetStyle=qtcurve setting in General section in .kde4/share/config/kdeglobals, with no effect.
Then if I install the kdebase-workspace package, the above setting works again.
Furthermore, I removed the kdebase-workspace package again, and put style=qtcurve in qt section in .config/Trolltech.conf, then Dolphin uses that setting, too.

So, it seems if kdebase-workspace 4.x package is not installed, KDE4 apps running in Plasma 5 won't read the widgetStyle setting in kde4 kdeglobals. But the style setting in Trolltech.conf still works.

Is this by design or a bug?