The auction house should remember the prices for all items you set forever.

I have no idea what the system is now, because results are wildly random.

Sometimes it does remember stuff.

Sometimes it forgets.

Sometimes you might have one item already listed (not just listed, but already listed), and you place another of the exact same item, and it doesn't remember the price.

This is a potentially awesome feature (the remembering of prices you set) that's greatly diminished by the wild inconsistencies in behavior.