1. Most likely the full time parent probably has the kid do chores or at least clean up after themselves. So if the part-time parent makes it nothing but a fun visit guess what happens... Kid doesn't want to live with mean full-time parent who makes them follow rules, kid wants to live with fun part-time parent. This will involve years of child putting full-time parent down and always sticking up for fun parent, begging to live with part-time parent making full-time parent feel bad.
2. Obviously a kid who doesn't spend 100% of time in a house shouldn't have to clean up after everyone while they sat around doing nothing. But the child should be expected to help around the house a bit, clean their room or shared playroom if they also made a mess. My point was you can't expect the kids who live in a home 100% of the time to clean up after themselves but when the step kids come around now step-daddy is cleaning up after his kids. Does that sound fair?
3. I may have gotten a bit off topic, I was think more of my situations. Like when the step-son drew on the walls, flushed toys down the toilet, ran back in forth across the street and almost got hit by a car (just a few examples) and never got in trouble. But when my son didn't want to eat all his veggies, he got sent to his room. I am sure I was not perfect in making everyone feel equal, obviously every parent is going to defend their child. I can honestly say I was hardest on my child at first, trying to make the step-kiddies feel comfortable but when I noticed the step-kiddies NEVER getting in trouble I was a bit disappointed.