My first question would be "Is it too warm where he has his free play?" I can only let mine out for about 20-30 minutes at a time as they seem to get overheated from all of the excitement of exploring and perhaps a bit tired.
At this time of year, I cannot let them out in the bathroom (the only room I can really chin proof), as the temperatures are close to 100 so they remain in their room with their new air conditioner.
I will be curious to see everyones responses.
Oh, and is your baby at all overweight? I have read that will affect their behaviour for sure.