Both . . .

Listening to the radio today, I heard an actor discussing two roles he has played. "Both characters are similar," he said.

The plural construction is correct, but to my ear, "both" suggests that they are doing something similarly, not that they are similar. 

I would have been happier if the actor had said, "The two characters are similar."

A similar example comes up in descriptions of negotiations. For example, "Both sides have conflicting objectives . . ." would sound better as "The two sides . . .."