That is how it works, very odd, but that is why doing 2 days of 500 calories in a row is probably not optimal.
I will admit here that I am no longer low carb, or even totally Primal. I do make sure that every thing I eat is homemade and not "packaged" but flour and sugar have crept in. I don't have a problem with them using the limitations I do now, and it makes me feel more like a normal person to have a piece of Blue Velvet Cake with Cream Cheese Frosting that BFF's DD made for us for Mother's Day. They have not caused me discomfort or binging issues or weight gain, so I am going to keep them as an occasional treat and let go of the feeling of deprivation that the idea of not ever having them again leaves me with. To me that is that major draw of the 5:2.