Qt does not synthesize click events for touchscreen

See my original report with many details in the KDE tracker: https://bugs.kde.org/show_bug.cgi?id=346871

Basically I have a Dell XPS 13 9333 which touchscreen.
Kernel driver is hid_multitouch.

The command "xinput2 test-xi2" shows me that the touchscreen only sends touch events, no click events.

I added qDebug() in qxcbconnection_xi2.cpp and saw that has_touch_without_mouse_emulation is properly set to true.

In such cases, I'd expect click events to be synthesized by Qt, but it doesn't work.

Tested with the owncloud desktop sync client (Qt5 app) and also Plasma 5.3.0 where touching the taskbar only moves the pointer but does not click.

This used to work in past versions, a few months ago, but I do not remember which. It is also likely that an update of the stack (xorg/xinput) triggered the issue.

But for now I had the feeling that Qt5 isn't working as expected.
I'll see if I can debug this further. Any help or hints appreciated as to where to put the qDebug() statements.