My Upside-Down Is Right-Side-Up... What.

[Marandart]

Okay, so I bought three upside-down catfish a few months ago. They're awesomely well behaved, never fight more than a little headbutting over food, and are growing well.
However, they're almost never upside-down. The only time they're even remotely upside-down is when they're clinging to a surface-- like under some decorations and in their caves. I have never, ever seen them free-swim while upside-down.
Is this normal, do I have freak fish, or are upside-downs never really upside-down?

They're cute as sin, but dangit, they're not upside-down. I've been swindled.

 

[winkle]

Do you have many broad-leaved plants or ornaments with overhangs or bits of bogwood?

I've only seen them in LFS (never kept them myself) but they seem to park upside down underneath things and will swim upside down from one parking spot to another.

 

[N0body Of The Goat]

If you see them free swimming right way up, besides when scouring the tank floor for food, I would bet money you have been missold Synodontis nigrita rather than Synodontis nigriventris (or the rarer and smaller contracta). My twelve only ever swim upside down unless its feeding time and even then they will graze upside down at the water surface if you feed floating food.