From the sample given in the manual – where Lorenzo, Jemma, and Felicita are all aligned – I assume this is just the way it works: only Guido gets shunted over to a separate column, implying that the core alignment is universal and that dual dialogue shifts the second speaker over in isolation (can probably be changed in secondary software if compiled to an editable format).
Can’t see a way to change this, but perhaps someone else can.
That or tech support: mac.support@literatureandlatte.com
Slàinte mhòr.