Why does my Quaker Parrot hang upside down

I am a wildlife rehabber and this bird was brought in with a broken foot. Our vet put a splint on the leg and he is fully recovered, but during treatment we found him to be a very calm and tame bird, nothing like a wild bird would act, and we do have wild Quakers here on the Texas coast. We have decided to keep him as he is so tame, he has even learned to say Hello and Pretty, Pretty from our other birds.

My concern is he has started hanging from the top of his cage most of the day and he even sleeps upside down. When we let him out, he hangs upside down on his play perches, my curtains, everywhere. He's not just leaning over, he is upside down, as in feet up, head down. Is this normal? Does he need something I'm not providing? He eats a variety of foods and we rotate toys as well as giving him play time everyday.

Has anyone ever had this problem with a Quaker before? Suggestions?

Will he display this behavior in an environment where it is difficult for him to hang upside down, such as a T-stand?

If he is clipped, see if you can arrange his environment where it is difficult for him to do so: perhaps a T-stand or a log in a room where he can't hang. Try putting him in the bathtub and observe him for a minute or two to see how he responds when he can't hang upside Does he pull the foot up just standing there?

Was it a broken foot or a broken leg? You mentioned a broken foot and then you said the Vet put a splint on his leg.