Partner makes a call and you know it wasn't correct

[bob jenkins]

As a general statement -- if it's a rules issue, change it; if it's a judgment issue, don't.

The OP has some elements of both -- maybe the guy just had a fast count. So, I'd be unlikley to approach the partner during the game to change it. But, if a coach complained, I'd be likley to ask my partner what happened. Of course, I might do something different if "game management" (phrase inserted to raise Jurassic's hackles) dictated.