We cannot add or remove private data members. This would change the size and layout of every subclass. We cannot remove public or protected member functions unless they are inline. We cannot make a public or protected member function inline. We cannot change what an inline function does, unless the old version continues working.
Some compilers mangle the access rights into the function name.
This is not a bug in Qt. You can safely ignore this message. QGDict uses bit field members to save space. When QGDict initializes its members, bits are either set or cleared. AND'ed with a mask and written back.