I'd bet good money he has learned that kidstuff plus poop equals mommy!
Some kids are regular--poop at the same time every day. Other kids poop willy nilly. He sounds like a willy nilly to me, and he has found a convenient way to take advantage of that!
Do you leave again after you change him? Or does he get you for the rest of the day?
Maybe you could coach him before you go, tell him that if mommy gets to exercise without changing a diaper, he gets to do a favorite activity when you pick him up (bubbles, a favorite song, etc.) I know it sounds like a stretch, but when my dd was 2, I would tell her at night to sleep through the night and she would! If I forgot to tell her, she was up at night. So they are capable of a lot of things we don't know about! (obviously, in Haakan's case).
He misses you! At least there's that...