Muscari grow leaves in the fall all the time. I live in zone 5 and mine have been up for weeks now. They always survive and thrive blooming and multiplying year after year. No need to worry about them. I have had tulips come up early in January thaws and as long as they don't get too far along they have always bloomed well. We had a really weird spring with temps in the 80's in March then after a month of that they dropped to the mid 20's. My early tulips had frost damage to the flowers but all bloomed and the later tulips showed no damage at all.
