You can think of the 2 Save as a last resort to save a 2. Thus, players are not allowed to perform a 2 Save on a 2 if that same 2 is visible in someone else's hand.
This is because the team does not actually need to save that 2 quite yet - they can save the other copy later on.
For example, in a 3-player game:
Bob has a red 2 on slot 5 (his chop).
Cathy has a red 2 on slot 3.
Thus, it would be illegal for Alice to perform a 2 Save on Bob's red 2.