Pekin make or female

[Almatt06]

so my first set of pekins were extremely easy to sex. My new three however I bought as adult females about a month ago. They were all completely flat tailed pale beaks. I put them with my three Muscovy male ducklings who had just feathered. About two weeks after one of the “female” Pekin had a curly feather on her tail.
A couple of questions....
Could it be a drake that was just younger than the farm owner thought?
Do females develop male like physical traits in the absence of a mature drake?
I’m going to include a picture of the tail in question.

 

[Brahma Chicken5000]

You have a drake

 

[PirateGirl]

I agree that it's a drake. Does the voice sound the same or different than the others? Usually the change in voice happens before the drake curl grows. How old is it? It may have been younger or may have been in molt. My drake is molting and lost his curl and looks like the ladies right now.