Sorry it's taken awhile to get back to you, been busy. Here is what I noticed from just testing it. I easy dev'ed a field in with alfalfa, going into winter at full ready to harvest. During winter I think DEC, it went back to growth stage 2. In april it went back to the first ready to harvest stage. I slept though 3 years and I had the same results. If it's still happening to you it might be a mod conflict.
Just wanted to let you know I tested the alfalfa this weekend and it works fine as you described. I think my initial issue was due to a mod conflict. Enjoy the map. Want to mention I like what you did with the soil map with the edges of the field. In my experience we always got lower yields off the edges.