When you are a spectator, if you have an item in your hand, and you open your inventory, the item in the little cahracter model's window is not in its hand it is more toward the center of model. This is very noticeable with tools since they are '2d-ish' it happens with blocks also, but is less noticeable.

To reproduce:
1) go in creative mode
2) get any item in your hand
3) go into spectator mode