0kg lost shown, but I've lost 2.5kg?

Hi,

It's been bugging me that on my home page MFP displays 0kg lost, and yet, when I first started tracking I weighed 78kg, and now I'm 75.5kg. So, I have, in fact. lost 2.5kg so far. It niggles at me very time I log in and MFP won't recognise my progress.
Any ideas why?

Thanks!