For these purposes, you can't have "medium spotting". You have spotting, or you don't. When you put in Light, Medium, or Heavy under MENSES, obviously FF assumes that you
mean "medium flow menses". And since Menses is your period, you're telling FF you got your period.
Just leave "spotting" under CM and remove "medium" from under menses (because this isn't menses!) and it'll go back.
Be sure not to put anything under Menses until you mean AF, and it'll be fine for you.
Oh, I see you fixed it! That's great. Just keep away from that menses box until you have to put something in. I've accidentally told FF that the witch showed up MANY times.