I watched S&P on the DVD with JMS's voiceover, and he sheepishly explained at the bathroom scene that the woman walking into it after Sinclair and Garibaldi left it was a mistake. So it seems that it wasn't a unisex bathroom. :-p

As for the alien bathrooms... I agree, there are some things We Aren't Meant to Know.

Morden becoming darker in Delenn's quarters was a good (and ominous) way of showing to the audience he's definitely not on the Light Side of the Force...