I'm attaching a second screen to my desktop, that resizes the desktop. During that action, shuttered up windows are resized to a very small size. This happens mostly with okular and dolphin windows here, but those are the ones, where I use the shutter function most often. Reproducible: Always Steps to Reproduce: 1. Enable shuttered windows 2. Shutter up some dolphin windows 3. Add a screen during the session Actual Results: Windows are resized spontaneously Expected Results: Windows keep their sizes I observed this with radeon, nvidia, and nouveau setups, therefor I expect some (timing?) related issue, where adding a secondary screen changes the desktop size of the main screen (the one, where the session started). It looks like the desktop resize is done as: remove main desktop area, add main+secondary area, and kwin chimes in in between and tries to resize windows to the minimum size. If that is the problem, kwin should delay the resize until xinerama operations are settled.
The action actually is delayed, but that doesn't necessarily cut it. Might be related to bug #161325, thus https://git.reviewboard.kde.org/r/121320/ Can you compile that patch and see whether it fixes your condition?
*** This bug has been marked as a duplicate of bug 161325 ***