QAbstractNativeEventFilter is no longer able to filter XCB mouse button press events on Ubuntu

Trying to capture mouse events on Ubuntu using a QAbstractNativeEventFilter and the xcb.h library seems to be broken. This used to be functional using Qt 5.4.2; however, when upgrading to Qt 5.5.0, the functionality breaks.

The source of this change can be traced to the following commit: https://github.com/qt/qtbase/commit/53d289ec4c0f512a3475da4bbf1f940cd6838ace.

There is an environment variable that can be set in order to retain the old behaviour; however, there seems to be no other way to capture mouse events without doing so.

The following code can be used in order to reproduce the issue: https://pastebin.com/W7JWrSgM