When I change plasma colorscheme the menubar and toolbar of Dolphin disappear
Can't reproduce. You change it in System Settings → Colors and then its toolbars disappear? What Qt version is this, 5.11.1?
Created attachment 113867 [details] dolphin missing toolbar and menubar
Created attachment 113868 [details] virtualbox missing toolbar
Exactly! When I change Color in System Setting then the toolbar and the menubar disappear in different applications like Dolphin and Virtualbox. See screenshots. I tried a clean install of Manjaro and I get the same behaviour.
I can confirm on Arch Linux, plasma 5.13.3. I applied several color schemes in sequence in system settings > colors without any problem while dolphin was running. However after I restart dolphin, both sidebar and toolbar were hidden.
Qt regression. See Bug 395988. *** This bug has been marked as a duplicate of bug 395988 ***