From the prologue of TSR, (Where Lanfear, Rahvin, Graendal and Sammael are meeting in Caemlyn):

"Golden bracelets clattered as she waved a heavily beringed hand generally behind her; the female servant quickly slipped the goblet into her grasp with a fawning smile mirrored by the man. Graendal took no notice. "So," she said gaily. "Nearly half the surviving Chosen in one place. And no one trying to kill anyone. Who would have expected it before the Great Lord of the Dark returns? Ishamael did manage to keep us from one another's throats for a time, but this . ."

The last sentence from Graendal about Ishamael keeping them from each others' throats explains that scene you describe. Rahvin and Be'lal both had plans for taking control of Cairhein. Ishamael was playing peacemaker.