QQuickWindow-based applications seem to hang on exit, sometimes resulting in a busyloop consuming an entire CPU core. Exiting via SIGINT yields the following backtrace:

#0 0x00007ffff4caa7ac in __lll_lock_wait () from /usr/lib/libpthread.so.0
#1 0x00007ffff4ca7d30 in pthread_rwlock_unlock () from /usr/lib/libpthread.so.0
#2 0x00007ffff4f1d782 in glXCreatePbuffer () from /usr/lib/libGL.so.1
#3 0x00007fffeff20a78 in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#4 0x00007fffeff04231 in ?? () from /usr/lib/qt/plugins/platforms/libqxcb.so
#5 0x00007ffff64beb93 in QOffscreenSurface::create() ()
from /usr/lib/libQt5Gui.so.5
#6 0x00007ffff79a3f44 in ?? () from /usr/lib/libQt5Quick.so.5
#7 0x00007ffff79a47e0 in ?? () from /usr/lib/libQt5Quick.so.5
#8 0x00007ffff79c0b9f in QQuickWindow::~QQuickWindow() ()
from /usr/lib/libQt5Quick.so.5
#9 0x00007ffff7a5f489 in QQuickView::~QQuickView() ()
from /usr/lib/libQt5Quick.so.5
#10 0x000000000040414d in ?? ()
#11 0x00007ffff53fab05 in __libc_start_main () from /usr/lib/libc.so.6
#12 0x00000000004064e7 in ?? ()

This happens on bundled applications like qmlscene as well as trivial ones, like:

#include <QGuiApplication>
#include <QQuickWindow>

int main(int argc, char *argv[])
{
QGuiApplication a(argc, argv);
QQuickWindow w;
w.show();
return a.exec();
}