Q_DECLARE_PRIVATE_D uses reinterpret_cast with the d member in the defined methods, which results in bad casting with the multi-inheritance subclasses of ServiceBasePrivate.
Switch to use KDNSSD_D instead of K_D to reduce risk of potential clashes.
This reverts commit e8f08295.
David, I would ask for a follow-up release of kdnssd 5.79, once approved.
Uploading for review while still testing some more locally, but almost sure this is the cause and fix.