"The Whole Story" bugged but not at Balthazar

[Euryon.9248]

This is now my 3rd attempt in this instance specifically for this achieve, and it's failed every time at the dialog between Caithe and Faolain. Each time, the achievement award flag is there while Caithe is speaking, then Caithe pops out, the achievement flag disappears, and then Faolain starts speaking. I did not move the entire time during the dialog. I can't think of a logical explanation why the flag would disappear in the middle of a dialog when I hadn't moved a pixel, but it's happened 3 times now.