I would take him to the Doctor and thoroughly discuss it.
The thing is, he is now 6 years old and does not seem bothered by it. AND you said that it RECENTLY has started happening- ie: his pooping on himself. WHY ONLY RECENTLY? Did anything happen to him?
Is he under a lot of stress or emotional difficulty? Any traumas happen to him? Is his overall development on par? Does he have any learning difficulties?
I would really talk to your Doctor. I don't think this is the usual that happens, at least with the poop, and at 6 years old. There must be a cause... biologically or emotionally.
All the best,
Susan