Riliane's sprite being there when she's meant to be dead may be the issue. I just went through the quest again with her alive, and didn't have that problem.
Edit: But on another note, for some reason when I enter the cave with Riliane after the suicide bomber blows himself up on the bridge, I can't go pass that narrow ridge where the bat enemy is. It's like there's this invisible wall. I can pass with other characters in my party, but Riliane can't be in it or I can't pass.