Hi Marcus,
I would still suspect this is something to do with the way the red and yellow wires are connected. The reason I think this is that if you turn the unit on and off manually i.e. with its own power button then this does not alter what power supply is coming down the red and yellow wires from your van. When you turn the ignition off however then one of the power wires usually goes dead. If you have the red and yellow the wrong way round then this is what causes settings to be lost etc. Assuming that your van does have both a switched 12 volt feed (usually on the red wire) as well as the permanent 12 volt feed (usually the yellow wire), then I would say that it is still worthwhile trying swapping these wires round (as lots of vehicles differ in terms of which way round these are connected).
There is a connector part way along both the red and yellow wires to your stereo that are provided to enable you to switch these two wires round - you can't do any harm but definitely worth a try to see if this resolves your problem - although as I say this does all depend on whether your van does have a switched as well as a permanent feed - which not all vehicles do - some only have a permanent feed.
Hope this helps.
