I can confirm these issues. As QT libraries seem to be particularly side affected, as a result KDE/Plasma is almost unusable while Java is running, with plenty of graphical glitches on each program: vanishing menu options, misplaced or missing controls, falied window redrawing... Also vlc is affected, unable to reproduce any video (audio works fine). As soon as Java stops running, all these problems are "magically" solved.
OTOH SDL and GTK-based GUIs work fine. openjdk-8 from testing does not show this behaviour.