QDialog::move can't move borderless window outside screen border

Description of problem:
Can't move borderless window outside screen edges. It works with Qt4 and with Qt5 in Windows. So it can be only Fedora/KDE problem

How reproducible:
always

Steps to Reproduce:
1. Unpack attachment archive
2. compile with qmake-qt5 && make
3. start with ./hello
4. Try to drag gray rectangle (borderless window) outside screen

Actual results:
Window can be dragged only on visible screen but stopped on screen edge.

Expected results:
Window can be dragged freely on visible screen and outside screen edge.