All achievements given at once, despite not earned

Today I handed in an assignment, and suddenly got the achievements for submitting 5, 15, 30 and 50 assignments all at the same time. I'm certain I haven't done more than 10 (not that I've counted).

While it looks nice on my profile, I'm not too happy about achievement badges I haven't earned and is nowhere near completing. I'd rather work towards it the way it's supposed to go and earn my achievements.