Did you get Monty from a petstore or breeder?
If it was from a breeder, I'd be willing to bet it's still a male and just didn't show you his hemipenes. Once a breeder pops and see's them, it's a guarenteed male, but sometimes mistakes happen with females because the hemipenes don't show and they think it's a female when it's actually a male.
So you see, males are rarely mistaken if that's what they're labeled as.
I adopted it from the place I volunteer at (herpetological society), and the guy who sold it to me just looked at the tail and said it was a male, so I wasn't even sure if that was correct.