Mine have just arrived today. I love 'em but the back slips very slightly - is this normal? They do feel like the right size everywhere else so was wondering whether this is just characteristic of the shoe if you know what I mean! Apparently they have to mould to your feet..a bit like Uggs. Sorry...as I'm typing I'm realising how tedious this all sounds! Anyway, any fellow Billow wearers I'd be grateful for your imput!