odd crate behaviour

I have a feeling that Amber may be peeing in the crate, even when she's with Holly. I was cleaning it earlier an underneath the cushion there was a slightly damp patch (but the cushion itself was bone dry). I wiped everything down with simple solution. I went out for a short time this evening, let the pups out, and checked. There was a slight damp patch again. Now, the bottom of the cushion is waterproof and I sluiced it down pretty thoroughly earlier- it's possible I didn't dry it as well as I thought I had. Alternatively, one of the pups has been peeing.

Only thing is.... there's a lot of friction between cushion and tray. I find it hard work shoving the cushion around in the crate, and noticed when I finally got it to my satisfaction that it was curling up against the sides of the crate. It was still like that when I came back. The crate is largish, but not so much that two dogs would have enough room to pull the cushion away, widdle, pull it back to exactly the same position and then arrange themselves....???? There's no damp, nothing dripping... I dunno where it's coming from.

Gremlins in the crate?!

Amber's excellent otherwise... accidents in the house (bearing in mind she's five months and has full access to all downstairs, such as it is) are few and far between.

Suggestions?