Here's a bunch of selected Conches (rank 2), some morphing to Djinns (rank 3).
After morphing, all the Conches are deselected. If multiple Djinns finish morphing at the same time they all stay selected, but any Conches still-morphing are deselected so any Djinns that finish later do not end up in the selection.
Another situation: shield cons (rank 2) selected alongside a shieldball (mostly rank 3) get deselected if an aspis finishes morphing to aegis (rank 1).
Here's a bunch of selected Conches (rank 2), some morphing to Djinns (rank 3).
After morphing, all the Conches are deselected. If multiple Djinns finish morphing at the same time they all stay selected, but any Conches still-morphing are deselected so any Djinns that finish later do not end up in the selection.
Another situation: shield cons (rank 2) selected alongside a shieldball (mostly rank 3) get deselected if an aspis finishes morphing to aegis (rank 1).