I first reported the issue on the forum, but received no response, so I file it as a bug.

Description
Working using Qt with a tablet with the stylus button simulating a mouse right button.
There are two problems happening when the stylus is on the tablet:

• When pressing down the stylus button: some tablet/mouse press events have QEvent::button() with Qt::LeftButton and QEvent::buttons() with Qt::RightButton
• After pressing down the stylus button and lifting the stylus: no TabletRelease/MouseButtonRelease is sent

Reproduce the problem

• Place the stylus on the tablet
• Press the stylus button (simulating a mouse right click button) (the press event with wrong button/buttons is sent)
• Lift the stylus from the tablet (no MouseButtonRelease/TabletRelease event sent here)
• Release the stylus button

Sample code
See the attached .zip file for a minimal application.
The application has:

• An area to test the tablet/mouse inputs
• A label widget to track the input events

The application also comes with a fix.

 Notes

• I tried to toggle the attribute Qt::AA_SynthesizeMouseForUnhandledTabletEvents but it does not change anything