I wrote a small test program:

#include <QApplication>
#include <QPlainTextEdit>

int main(int argc, char ** argv)
{
	QApplication app( argc, argv );
	QPlainTextEdit p;
	p.show();
	return app.exec();
}

1. Run the program
2. Call the popup(context) menu (right mouse button click)
3. Throwing him(left mouse button click at free space)
4. Try again call popup menu
5. Expected popup menu does not appear