Go to Settings, iTunes and you can set the order. There is even an option where you can set any order you want to by holding the select button down, and moving the shows up or down.
I bit the "Time Machine" bullet earlier and restored the Mac running iTunes for my Apple TVs. I'm gonna sit on v10.5.3 (and nicely ordered TV Shows) for now.
They are being listed in the order they were added to iTunes by the looks of it.
Yes, the oldest are at the top and the newest are at the bottom.
You may be different, but mine are definitely being listed in the order they were added. That is why, if I add them in alphabetical order they end up sorted correctly.
iTunes 10.6.1 released today supposedly fixes the issue.