I'd check around the bottom. Look for little "sore" or "blister"-like projections from the stalk because it may be producing new heads. If I remember correctly, then that's what my single frag did back in the day. A week later it was 6 heads.
That is so weird. Have you changed your bulbs or anything? Mine is retracted when the light is off and when I moved the powerhead placement a week ago it stayed closed up for a day or so. I hope it is just what Adept suggested. I don't remember mine doing that when sprouting new heads but I probably wasn't paying attention.