If the hinges were up and springs were relaxed maybe one got stuck together or something? Like it was painted with the hinge? The hinge moving points are gummed up with paint?
I am thinking you simply didn't get it back exactly as it was before.
You know the same thing happened to me recently. I had the springs and hinges powder coated on my car that was painted together and aligned before they were done. I went and put them back on right on the marks I had left and darn if the right side wasn't up in the back. It took a little more adjustment to get it down.