Comment # 6 on bug 1001790 from Wolfgang Bauer

(In reply to Wolfgang Bauer from comment #5)
> OTOH, there may have been a bug in Plasma/powerdevil 5.8 beta (which we
> currently have in 42.2), unfortunately I see no change in 5.8 final, but I
> cannot find an open KDE bug report about that either.

FYI, I just had a look in Plasma 5.8 beta on my 13.2 system, and powerdevil
does seem to inhibit logind properly:
test@amiga:~/Desktop> systemd-inhibit --list
...
    Who: PowerDevil (UID 1000/test, PID 7981/org_kde_powerde)
    What:
handle-power-key:handle-suspend-key:handle-hibernate-key:handle-lid-switch
     Why: KDE handles power events
    Mode: block

As this is a desktop system, I cannot test whether lid close actually does
respect KDE's settings though (and 13.2 has a much older systemd version
anyway).

But I would suggest to look at the output of that command and see whether you
have a similar entry.

If not it's a problem with powerdevil I suppose.

If yes, I would try to set "LidSwitchIgnoreInhibited=no" in
/etc/systemd/logind.conf and see if it helps.