When the FNMA premium went up to ~.05 I said it was in parity with the capital distribution from FMCC (thus it would come out of the price of the stock, like a dividend) which - if you are pair trading one long and short FNMA/FMCC you'd be expected to pay.
Clearly something has changed or we're simply getting a squeeze out of nowhere. Market maker either way is offsides or no longer neutral.