This time it surpassed itself.
This time it failed to drain. Period. And of course the door locked itself and refused to budge, which is understandable considering the drum was a third full of water still.
The fluff filter was not clogged (as we found out when the landlord came around with a suitably hefty wrench to loosen it after it got overtightened by mistake), and this time we caught the water before it could flood Dom's room again. So, drain water out the fluff filter hole, inspect fluff filter and find it's lacking in fluff, screw filter back up and run a spin cycle to dry the clothes out a bit (having verified that the door now opens)
Washing machine makes a few half-hearted attempts at spinning, mainly due to the load being a bit unbalanced, all the while failing to drain any more water. So we stop it, run a drain cycle (which now unlocks the door) and I extract the clothes to discover half an inch of water still in the drum.
Flick it on drain cycle *again*, and it hums away merrily while completely failing to drain. So we now have a washing machine that while it will wash, and it will spin, it won't drain. Hmm.