Shadow draws for Qt4, but not for Qt5. Reproducible: Always I'm using Gentoo ~amd64. Mesa with radeonsi driver, xf86-video-ati. Plasma 5, KWin with GLX & OpenGL 3.1
Thanks for reporting. Sadly I cannot reproduce and have no clue how to debug. Besides, the code is very similar (well: identical), between breeze for Qt4 and breeze for Qt5. Can you first post a screenshot of the issue ? (sorry for being slow at answering, i have been busy with other stuff)
Sorry, it was Gentoo bug (already fixed), I forgot to close it :(