My puppy pees in the crate when we leave for errands even though he knows to sit by the door when he needs to go potty.

I have a puppy that is 15 weeks old. I got him a month ago, and was able to housebreak him in about 3 weeks...at least I think so because he now sits by the outside door when he needs to go potty. I can even leave him outside of his crate during the night. He sleeps in the bathroom, and has never pottied there. He waits until the morning when I go outside with him.

When my wife and I leave the house to do typical errands, we put him in his crate because we still don't trust him to be unsupervised. However, when we return we see that he has urinated in his crate. This has happened nearly every time we leave. We don't leave the house for hours, and before we leave we take him out to potty which he does. I find this strange because he can go the whole night without urinating in his space in the bathroom. Any ideas why this is happening? His crate is not too large for him.

By the way, I should mention that we also have a 3-year-old dog that is completely trustworthy and can be left in the house without any supervision. This 3 year dog has never caused any damage in the house when he is alone.