1) Actually talking to Mellisan at the start, before she talks to you herself yields a conversation that ends up with two Imoens, part of her dialogue from after you use the pools, talking to Irenicus twice, no Bodhi, and Sarevok's dialogue with Mellisan.
*This problem can also be seen in Brynnlaw, where talking to the cook yourself before she initiates dialogue herself ends up with you giving her the potion the first time, then having to say nothing the next time, which leaves her stationary.*
2) When the Five appeared, Mellisan joined them. After I had killed Sendai, ANOTHER Mellisan appeared, with her 'To the victor go the spoils' line, and attacked me.