Do we really want to add Breaks/Replaces for experimental versions of the package and carry them in unstable? libqwt-qt5-6.3 has: Breaks: libqwt-qt5-6 (<< 6.2.0-1~) Replaces: libqwt-qt5-6 (<< 6.2.0-1~)
I suggest to finally file for a transition slot.
