One of my female ducks has damaged feather follicles on her tail. Some of the feathers are flatter at the base and curl up and back to her body - and look very similar to a drake feather. She molts them yearly, and at the moment she doesn't look much like a drake, but at first I was sure she was changing genders.
I don't keep drakes so I don't know what drake feathers look like at the base, but my duck's odd feathers look different from her regular feathers.