QDrag::exec doesn't work between different processes

When performing a dragndrop between 2 processes (running the same program), the QDrag::exec return value is 0 (Qt::IgnoreAction), but running the DND in a single process, QDrag::exec returns a sensible value (for example Qt::MoveAction).

The issue seems to be in Qt5, if running the same program with Qt4, it works fine.

To see the problem, build the attached source code, run 2 instances of the program, it will show 2 windows, and do a drag from one to the other. The issue doesn't appear if drop on the same window where it was dragged.