How can I get my puppy to stop wetting the bed?

I have a 15 week old Labrador puppy. We thought we had reached the point of being housebroken/crate trained since we hadnt had an accident inside the house for over a month.

Earlier in the week we bought him a nice dog bed for use outside the crate, so he can lay on the floor in the living room. He has been laying in the bed every evening since we got it. Last night I looked over at him and he was squating and peeing on the new bed. So we washed the bed and decided that it was an isolated incident.

A bit earlier tonight the same thing happened. I looked over to him squating and peeing on the freshly washed bed.

Why is this happeneing? How can we make him stop permanently?

We let him out for potty every few hours and he is able to hold his bladder for atleast 7 hours, so I know that he has sufficient bladder control.

Usually if he needs to potty he will go and sit by the door and wait for us to open it.

I am becoming frustrated and really would like some help on this.