Completing the diary for the day

I used MFP a while ago, and it just would not let you complete your diary if you'd eaten less than 1,200 for a day, giving you an error message about not eating enough if you tried.

Today however, I accidentally hit the button while scrolling and it gave me the usual "in five weeks you'll weigh XX" message. However, I had only eaten 1,068 calories. Why does it now allow you to undereat by so much?