BP not pooping or peeing inside enclosure

[Luvyna]

TL;DR: Ball python holds his poop and pee until he has a sausage butt, then goes outside of his enclosure. Why?

I don't know if BPs are capable of this kind of forethought, but I could swear that mine waits until he's out of the enclosure to relieve himself. In the past 3 months, he has "decorated" me and various pieces of furniture in the house 3 times, and has not gone in his enclosure a single time. (He also had to be soaked to get him to poop during this period, I think he was constipated and I am still trying to find out why that happened, have been keeping humidity between 65-75% and feeding him wet rats to see if that helps.)

He usually waits until I'm not holding him and he's just laying in my lap or on my stomach when I'm sitting or lying down. Then he'll stretch himself out and pee on me when I'm not paying attentionThis is my fault, really, because I ignore the warning signs like a slight sausage butt...etc. lol and it makes sense that handling helps move things along. I've learned my lesson now and next time I see a sausage butt he is staying in his enclosure until he either goes or he is getting bloated/it's been too long and he needs to be soaked.

There have been a few times when I caught him lifting his tail and rushed him back to his enclosure. Not sure if that throws him off or what but once he's back inside he refuses to go. I check on him several times a day and always check the temps, humidity, water, and look for urates or poop. If any of his substrate is soiled I clean it right away so it never stays dirty for more than a few hours at most. I'm just wondering why he isn't going in his enclosure anymore the way he used to, is it abnormal for a snake to wait until they develop a slight bulge around the vent area? Could there be something wrong with the enclosure or husbandry that is causing him to go outside instead of inside it? Or has he just decided he'd prefer to go outside (I hope not)?