Qt 5 refuses to handle clipboard events if application runs in debug mode and shows a qWarning message "Cowardly refusing to send clipboard message to application under debugger...". I do not know about the exact reason for this. I also do not know if this behaviour can be changed.
However this behaviour is fatal for an automated testing application that simulates GUI actions. These GUI actions also include clipboard handling.
In fact with Qt5 it is not possible to develop a fully featured GUI testing automation anymore since it can not be run in the debugger without fails.
If there is any other solution it should be considered!