My Moutarde Rouge Mentis flowers very quickly

After sprouting and growing to a usable size the flower stem of the Moutarde Rouge Mentis (a leaf mustard variety) is also already there. I can only pick leaves once or twice before it flowers. To what I have read online I should not pick leaves after flowering any more, because they turn bitter. Am I doing some thing wrong, or does this variety just bloom very quickly? The seeding package states that I can sow and harvest the Moutarde Rouge Mentis al season long.

I will let the Moutarde Rouge Mentis bloom and hope I can harvest seed from it.