Animations using the Animation object AND changing the DesiredAngle of Motor6D?

Okay, so I have this really confusing problem that's probably messing with the core coding of Roblox more than it should be. Basically, I have custom characters that include stuff like multiple limbs. I'm using Motor6D objects to animate every limb available using the old Roblox Animation script (the one that changes the DesiredAngle). Now, these custom characters are also planned to use the Animation object to do attack animations (stuff like swinging claws). Because this requires a HumanoidRootPart, I added it to the model and welded the Torso to it.

So I made all of that, and tested it. The problem is, while animations using the Animation object works fine no matter what, the old animation script that is moving the limbs won't work under certain conditions. Here is what I learned through testing:

1) If I'm testing in Test>Play Solo, the animations work fine.

2) If there is a server with no players in it, the animations work fine.

3) Likewise, if there is a server WITH players in it, the limbs will no longer move.

4) The Motor6D's are changing the DesiredAngle and the CurrentAngle all the time, but that doesn't mean the limbs are moving.

5) If I anchored the HumanoidRootPart (which results in a cool/useful glitch*), the animations will continue to work.

LINK TO THE MODEL http://www.roblox.com/E-item?id=150955815

*If you anchor the HumanoidRootPart, then server mode will register a character as if it's stuck in one spot. That character, however, will still be able to move around on the player's computer as if it's not anchored. Once you unanchored the HumanoidRootPart, the server will 'teleport' the character to where the player is on their computer. It's like putting a clone of the character in workspace, and moving the actual character to the CurrentCamera. It could make an interesting puzzle game or some sort of "ghost" feature like in that Call of Duty game.