Still have my Magpie ducks. They are still a work in progress. I have a mix breed somewhere. I thought that I figured out who it was and culled him out of my flock, but I hatched out an odd ball this year and now I'm back to trying to figure out who it is. I'm planning on a major cull sometime but haven't seemed to fine the time to do it.
What kind of oddballs are you hatching? Based on the genetics of how it would happen, I might be able to help you narrow down who your culprit is.