KDE Applications Use Oxygen Widget style eventhough Breeze is selected (Plasma 5)

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I could resolve the issue by uninstalling "appmenu-qt5" package. After uninstalling the package and rebooting, the styles are back to normal.

The issue is back again but in a whole new way. The Qt4 applications reverted back to Oxygen instead of Breeze style.

1. appmenu-qt5 is still not installed as it breaks the whole decorations and applications.
2. kde-style-breeze-qt4 package is installed in the system.
3. "Breeze" style is now missing from "Qt4 Config" (see attachment).

What am I really missing?

I have this bug after upgrading Ubuntu to 15.04 Vivid. After debug with strace, i deleted ~/.config/Trolltech.conf, "Breeze" theme appeared in qtconfig-qt4 and now Qt4 application looks good. Maybe it help.

@Aleksandr Loktionov, That worked for me. Thanks a lot.

Deleting Trolltech.conf seemed to work for me too but not immediately. I deleted it within KDE and then when I logged out the logout failed. I rebooted, logged back in.. and it wasn't fixed. I later logged out and back in again, and then found that my icons were working. Perhaps it takes a couple times for it to rebuild the config.

If the package appmenu-qt5 is installed, Plasma is broken. This is due to appmenu-qt5 installing a /etc/profile.d/appmenu-qt5.sh which sets the QT_QPA_PLATFORMTHEME env variable. By having that loaded into the session the qpt plugin provided by plasma-integration won't be loaded.

I am working on removing appmenu-qt5 from default installations: see bug 1612767 for that.

Status changed to 'Confirmed' because the bug affects multiple users.

The possible workaround is unsetting `QT_QPA_PLATFORMTHEME` in ~/.profile file. A workaround is described in this askUbuntu answer written by me http://askubuntu.com/a/817066/61218

You put these in ~/.profile

## Fixing QT style override problem
if [ "x$XDG_SESSION_DESKTOP" == "xKDE" ]; then
    unset QT_STYLE_OVERRIDE
    unset QT_QPA_PLATFORMTHEME
fi

if "x$XDG_SESSION_DESKTOP" == "xKDE" doesn't work, use "xplasma" instead