Okay, So I think the next step might be to remove the tumbler ("drum") from the machine, so you can see what's happening inside the waterproof outer drum/enclosure.
EDIT: Mmmm.. that might end up being a lot more complex that what I'm used to, so you'll probably not be doing that.

Based on observations thus far, I would guess that perhaps the drain cycle is leaving water/suds in the outer drum/enclosure, but not so much that the puddle is visible in the inner drum.

So perhaps there's a drain level sensor or something that's not reading correctly, or (again, sorry) there may be a partial clog of the drain such that it takes longer than the timed cycle allows for.

There's probably 5-10cm or so of space between the tumbler drum and the outer drum, so lots of room for soapy water to linger if not drained completely.

Removing the tumbler drum will give you full view/access to the main outer drum/enclosure, drain and fill openings, etc. So easy to check for clogs and things, as well as to give it a general cleaning while access is good.

You'll have to google for "how to" do that, but it generally involves removal of the face of the machine, which can be held by some very strong spring clips or other mechanisms. Then the opening at the front will be large enough for drum removal. There is probably a very strong nut/bolt fastener hiding behind trim at the back/centre of the tumbler drum. Undoing that will release it for removal, though it may appear to be "stuck" and require some directed force for removal.

Best to just google it.

I did that just now, and found this link for an easy way to check the pump:
http://www.fixya.com/support/t1626607-zanussi_iz_12_pump_access

There are lots of other links for disassembly etc.