It's likely the same as bug#1096806 and https://bugreports.qt.io/browse/QTBUG-68449, I suppose. A fix for the X server has been proposed here: https://lists.x.org/archives/xorg-devel/2018-June/057020.html OTOH, there also will be a fix in Qt 5.11.1 that should avoid the problem: https://codereview.qt-project.org/#/c/231408/