That's interesting Zac. I logged VH-QOI this morning at 0730 as Mode-S only, not as full ADS-B (no lat & lon transmitted). Was away last week so my last log for VH-QOX was 16 March (Mode-S only).
Have a look at this subject in the FR24:-
http://forum.flightradar24.com/threa...ll=1#post49528
that might explain how you may have seen these two Q400s on FR24 due to the auto MLAT application.