@mystikmind,
If my ex-wife sent her sister to pick up my daughter... I would support that. When it is her time, she is responsible for our daughter. I don't interfere. Maybe my ex-wife is working late, or maybe her sister is in the area. There is no reason for me to be a jerk about it.
I care about my daughter, and supporting her mom in any way I can is good for my daughter. Being an asshole about whatever is "stipulated by the court" would be ridiculous. My ex feels the same way.
My ex and I are co-operating, we support each other when it comes to our daughter. I haven't worried about the "court stipulation" in years. I kind of remember what it says... but we aren't being jerks about it. It was kind of funny, we had a hard time negotiating it during the divorce, but we both soon got over it and realized that fighting didn't do anyone any good.
When my ex-wife is working for a weekend she is supposed to have my daughter, I cover. When I want to take my daughter for a week to New York (as I did recently) my wife supports it. The parenting plan we fought over during the divorce quickly went out the window when we realized it is far better to just put our daughter first.
If you care more about fighting with your ex, then you care about cooperating for the good of your child you are screwing up as parent.
People who fight over "court stipulations" are failing as parents.