Water comes in and gets pumped around - if you open the door after a few minutes you should be able to see it splashing about for a second or so - opening the door stops the circulating pump but it doesn't cause the machine to drain - well certainly not on my machine.
Sometimes the spray arms in my machine get blocked with paper lables of jam pots etc. So it's worth checking the spray holes that make them spin round - providing of course that the circulating pump is running.
There are two pumps - a weak and feeble one to drain the machine at the end and a more powerful one to make the water circulate and clean the dishes - I would guess that the circulating pump may be a cause of your dirty dishes - but I just guess...
Peccavi, April 2009