Not seen it personally, but heard of it. It's to do with hormones and those affected are usually older does I believe.
Here is one I shot last year
I have a doe on a piece of ground I have with a 5" antler in velvet over her right eye, I also shot one with raised pedicles last season. It's caused by a hormonal imbalance (testosterone production if I remember rightly, the same as old women getting moustaches) as the doe gets old. The one I have at the moment has a single follower this year and is in good condition. I will try and get some photos to post of her one day.