XCB: Stuck in always "clicking" state in QT5 apps with Wacom pens

I encounter a very nasty bug using the just released Krita 3 (https://krita.org, based on Qt5) : I get stuck in an always
clicking state with QT5 apps, meaning when the bug occur, I'm clicking
everywhere by simply moving the cursor hover any interface. So everything become unusable and I have to log off my session or reboot to temporarily resolve it. If I use the Plasma desktop, everything become unusable.

As far as I can test, it seem to be Linux specific, and started with Qt5 (Krita 2.9, based on Qt4, wasn't affected).

A video : https://drive.google.com/open?id=0B-5J--XsvWh-LWFVM0pjRTdSa0E
(download to see it full res)

How to reproduce with touch events :
1/ pen away from the tablet, zoom or unzoom with a touch pinch
2/ holding the touch event, let the pen enter tablet detection HOVER THE INTERFACE (not the canvas)
3/ Most of the time the touch event is stopped, but the pen is left in this "drag and drog" state, clicking everywhere. Some times it doesn't happen... may be dependant on the exact input when the pen detection start or where the cursor appear on the interface, I can't define it more precisely now.

A variant without touch events :
1/ pan on the canvas with the middle mouse button
2/ while panning with the mouse, let the pen enter tablet detection over the interface
3/ pen cursor is locked in an "always panning" state until I trigger a right click or middle click with the pen

I already filled a lengthy bug report on Krita bug tracker :
https://bugs.kde.org/show_bug.cgi?id=363225
and continued the discussed with the Linux Wacom maintainer Jason Gerecke, who was able to reproduce and confirmed it's probably a Qt bug :
https://sourceforge.net/p/linuxwacom/mailman/message/35151033/

"Based on the logs and the information you've provided in the bug, I'm
tempted to agree that this sounds like an issue with Qt rather than some
other layer. It almost sounds like Qt is dropping events from other
devices once the pen comes in proximity, and doesn't always properly
clean up their state by releasing any buttons that may have been pressed."

might be linked to this bug : https://bugreports.qt.io/browse/QTBUG-27634

I attach all the logs I've been able to gather until now.

I insist, this is a really grave bug : when it occur, everything based on QT become unusable until logging off or rebooting. I'll really appreciate any guidance on how to solve this.

Thanks in advance for your lights and guidance !