The presence of Q_PROPERTY in the private section of a class causes subsequent members to be treated as if they were was public:

#include <QObject>
/// Foobulates grobs.
class Foo : public QObject {
  /// Indicates grob's rombulation.
  Q_PROPERTY(bool prop READ prop)
  int q; // treated as if it was public, but it's private
};

$ doxygen -g Doxyfile
$ doxygen > /dev/null
x.h:6: warning: Member q (property) of class Foo is not documented.

Removing the Q_PROPERTY line causes the issue to disappear.

The expected behavior is that a Q_PROPERTY entry does not change the access of the subsequent members. The Q_PROPERTY is a moc macro and it has an empty body.