I remember while I was messing about with settings on dashboard using the steering wheel buttons. I came across with something like 'Unlocking' - 'Unlock passenger door or unlock all doors'.

Previous owner must have left it, when I bought my Leon it was the same, but the settings had sorted it.
 
Sorry to pull up an old thread but I have today just changed this switch and can confirm it fixed the same issue that the op had.

The new switch comes with a logo of paddock as opposed to the logo of a key. The switch cost me £22 from my local Seat Dealer which was considerably cheaper than what people on ebay were asking for the same switch.