It's probably not what you meant to ask, but yes it's true and I have done it. However, one passport was a personal (blue) passport one was an official (maroon) passport.

I have not heard of anyone having two valid blue US passports at the same time, but there's no reason why I would have. I have not tried to to get a second blue US passport while maintaining the validity of the previous passport, and if I tried, I would expect to fail.