Background transparency not applied when restoring session

[trmdi]

Please read cfeck's comment:
https://bugs.kde.org/show_bug.cgi?id=362857#c17

How about that in Kvantum?
(See my comment https://bugs.kde.org/show_bug.cgi?id=362857#c16)

[tsujan]

Wherever I've installed KDE, I've disabled its session restoring because of such issues.

As you mentioned, the problem isn't limited to Konsole. For example, I use KWin under LXQt and add a short delay to lxqt-notificationd startup for KWin to be started before it and its blurring/translucency to be applied to notification popups. Fortunately, KWin starts before other LXQt components.

With KDE session restoring, there's no guarantee that apps start after KWin. Many Qt apps aren't KDE apps, so that adding KWindowSystem::compositingChanged() to their codes isn't an option, of course.

All in all, this issue isn't related to the style engine and can happen with all. Kvantum checks for blurring only when the app starts (checking it again and again would take extra CPU time) and if it isn't available at that moment, it supposes there's no blurring. The same is true for compositing: it's checked only at app's startup too,