gender confusion

Question
I recently bought a red eared slider and had sexed it as a male because of the long nails, shell shape, and the position of the hole in the tail. But yesterday I bought another turtle, also classified as male and put it in the same tank. the smaller turtle immediately mounted the other and the original turtle was receptive. They both also have engaged in this claw fluttering at each other's faces at the same time. I was wondering do males behave like this towards other males or did I sex the first turtle wrong? And if I did do this wrong, then why does the "female" have such long claws?

Answer
Males do occasionally behave this way toward other males.  Some males emit pheromones that mimic a female's, perhaps to deliberately confuse other males so they have better luck with the real females.

It's probably best not to house them together.  They may become aggressive.