I just upgraded to Kubuntu 15.10 (KDE 5.4) and I can't seem to properly close dialog and configuration windows. As I logged in kdewallet prompted my password, but after I put it in the window was still showing. I cannot click it, move it, or close it. Same for every settings window I open.

Rebooted and problem persists. Help?

run "kcmshell5 kwineffects" and disable the translucency effect, report whether that changes anything (try to re-cause the problem with a re-login
)

That worked. The windows appear and disappear as I enable and disable translucency. This is very confusing and not obvious. Should I report it as a bug? Is it an issue with the translucency effect?

Thanks for the temporary fix.

https://bugs.kde.org/show_bug.cgi?id=342716

It's hard to say where the problem actually is, but it's been reported before.
It's apparen that the translucency effect keeps "some" windows referenced.

Since it's limited to "dialogs" that may relate to
a) the dialog translucency implmentation (do you use the dialog transucency setting?)
b) some specific behavior of those "dialogs" (Qt5 only? Modals only?)