Author Selena Kitt has an entry on Amazon's latest follies in filtering.

I honestly don't mind if 'adult' titles end up in 'adult,' but having a gay couple on the front cover should not automatically mean 'adult.' Not even close.

EDIT: Fishing around it seems the case isn't as clear-cut as Selena made it out to be. I still wish I knew how Amazon filtered things, though! (Smashwords has an adult filter where you just push a button. So handy. Get on that, Amazon!)