Just reporting an annoying bug (since 4.7.x) which has been recently fixed upstream. The upstream bug is https://bugs.kde.org/show_bug.cgi?id=275286 while the fix is https://projects.kde.org/projects/kde/kde-workspace/repository/revisions/77b1374b99ee91d23d8802dd1dec9a5f630e919a in comment 102.
Added in plasma-workspace-4.7.3-r6 (it's in 4.7.4 anyway).