Do you just let you puppy “go” in the play pen?

I have an almost 12 week havanese puppy and he’s been doing great with outdoor potty training so far! Runs to the door to signal when he has to go and very little accidents in the house so far

The only place he does “accidentally” pee is while he’s in his play pen. I was hesitant to put pee pads bc of chewing and also I didn’t want to reinforce peeing on such soft material. The pen does have a kind of thick tarp under it so it’s manageable but I’m just wondering why this is / if it’s normal for them to just go in his pen?

Sometimes when I leave the playpen door open he’ll zoom out and still go to the door which I love / praise but sometimes he doesn’t and just stops and pees while staring at me lol

Is this normal / am I expecting too much from him lol he’s just been doing so well with potty in my head this feels like setback