Looks like it might be a limitation/bug. The behavior is the same with 5.6
You should go to the bug report system to see if it's something known. If not please consider opening a new report providing a minimal compilable example (not just the code files) to reproduce the behavior.
That doesn't really help. I know the difference between the 2 devices.
The issue seems to be in the path and maybe the resulting timing Qt (QWS to be more precise) gets the XY position compared to the path over which it gets the click events. This seems not to travel the same way from DFB to QWS.
Still have no solution for this.