Is the Multicity booking tool broken?

[exceladdict]

Encountering a new fun game on the multicity tool today. On the particular set of dates I'm looking at, searching PER-FCO/CGG-PER offers up the QF flight to LHR then BA to FCO on the first leg. When I click 'show all flights', with the goal of swapping to the QF-coded-EK option, it errors out. It seems to work fine if departing the next day though?! (the itinerary prices on ITA and google flights, but clickthrough to the QF website doesn't work).

One alternative is searching PER-DXB/DXB-FCO/CDG-PER, which allows me to select EK the whole way through, as desired. If I booked this, would there be any issues with EK not checking the bags the whole way through to FCO? Could always call up I guess.