My two year old female Mallard had a sex change?

[July the Caesar]

I have an issue with one of my Mallards. Supposively when I purchased my Mallards two years ago I had ordered sexed three females and one drake. About 8 months ago, I noticed that one of my females was beginning to show signs of a drake. Curly tail feathers and a tint of green on the crown but other wise female characteristics. Her name is Maxine after the Andrew sisters and the other two names are Laverne and Patty. Never thought much about Maxine since she never once tried to mate with the females. In fact, she at times laid in the nests. I thought it was odd that it took so long for her to change over to being a drake. My Drake, Mally same birth date as the females, had his colors, curly sex feathers, and green crown with ring around the neck about 5 months after birth. After 2 years she is still changing. She is not a full fledged drake. Another odd thing is that Maxine, like the other females has a yellow beak. My Mally has an orange beak. I have been confused about Maxine her/him for a long time. She doesn't mate with others and she appears to be a loner although she likes hanging out with the newest 5 month duckling additions (2 females, mallard and pekin). But otherwise very shy. In fact she doesn't quack much at all. Need help to know why she is changing and it appears to have both sexes? I will post pics of Maxine or Max?? Its crazy....but did she have a sex change???

 

[Herdcutter]

Drakes always have the curling tail feather.

 

[July the Caesar]

Ok what about the beak color? Maybe he is in slow growth but it is strange. He doesn't full drake. And doesn't mate at all. Sits in nesting area like the hens.