Medicare premium penalty for filing federal taxes, married, separate.

Hello, I was wondering if you could talk about why there was a penalty when paying Medicare part B premiums if you are married and filed taxes separately. In our income range we would pay $67 each per month because we filed separately right now we each have to pay $326 per month. Why is there a penalty? The only reason I filed separately is because my husband is terrible about paperwork and never filed on time and paid interest and penalties but we each paid our taxes and I feel it is unfair to charge five times the premium just because we filed separately.