If the developer mistakenly tries to inherit QObject second in a class with multiple inheritance like this :

class PointItem : public QGraphicsItem, public QObject
{
Q_OBJECT
};

the following error is produced when make is ran on the makefile generated by QMake :

main.cpp:20: Warning: Class MyWidget inherits from two QObject subclasses QGraphicsItem and QObject. This is not supported!

QGraphicsItem does not inherit QObject, so this error is incorrect.