Reason is very likely that the state is broken after updating the window stack or the signal received/handled queued. Thus the effect keeps windows translated and on re-invocation will cause a second translation or whatever - at least it's not getting better. Reproducible: Always
Actually was more stupid.
Git commit e0c3b4eed35b6db0f32cb6aefe6f5b4cfd96172d by Thomas Lübking. Committed on 15/05/2015 at 19:58. Pushed by luebking into branch 'Plasma/5.3'. window aperture always needs to cancel even if the window is invisible fade out instead of NOOP or "restorage" REVIEW: 123636 M +20 -1 effects/windowaperture/package/contents/code/main.js http://commits.kde.org/kwin/e0c3b4eed35b6db0f32cb6aefe6f5b4cfd96172d
Git commit 0da58680fc805175d041104f47a800dde85586fd by Thomas Lübking. Committed on 15/05/2015 at 21:55. Pushed by luebking into branch 'master'. window aperture always needs to cancel even if the window is invisible fade out instead of NOOP or "restorage" REVIEW: 123636 M +20 -1 effects/windowaperture/package/contents/code/main.js http://commits.kde.org/kwin/0da58680fc805175d041104f47a800dde85586fd