Well Here's my test results!
Popo himself is perfect
Well almost. He can't grab, but he CAN be grabbed!
Also his TransN index is the same as Amy's hips, which totally destroys every animation I have so far.
I noticed some things that might give a little insight on this glitch though.
1 - The moment someone initiates a throw on amy popo, her lower half instantly bends at a 90 degree angle, despite the fact that she has No animations whatsoever. This includes having no TransN bone or ThrowN bone. (the game was reading something else cause she didn't stay in a complete T stance) But what... is the question!
2 - This bend wasn't at the top of her legs but around her waist or stomach.
3 - They have no bones named the exact same (i'll double check to make sure) and in brawlbox, her being thrown animations play like all the others, as a t-stance. In game, like mentioned above, it's a bent T-stance, like an "L"
Therefore, I'm confused outta my mind, but I figure I post this so maybe, someone else can get something I'm not