No no no no no. The diffs are supposed to rotate, but not 'slip'. By slip, we mean that both sides of the outdrive can go in the same direction when the middle (gear) part stays still (or, the outdrives stay still but the middle part can move).
If you can find a way to hold both outdrives firmly (two allen wrenches, but some people use something like a Team Much More diff adjustment plate) and turn the middle gear bit with your hand, it's slipping too easily.
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