Water leak on dash at A pillar - 2011 E70

[Acinomer]

It was very disconcerting to open the car today and see this stain on the leather dash from an apparent water leak.

It rained very heavily two nights ago while driving and I'm guessing that's when it happened, but I have no idea where it came from. I pulled the A pillar cover just now assuming I'd see some water staining, but nothing. What's weird is that the padding under the leather is completely flattened, as if the water dissolved the foam or backing—there's a little ridge at the transition.

Any thoughts on what could be causing this? Coincidently, I'm going into the dealer on Monday and will certainly have them look into this and hopefully replace the dash, but I'd like to go in informed. I have 6 more weeks of warranty. Woo-hoo.