The problems were that MS QC every piece of DLC before allowing it onto the marketplace. It was sent to MS from IW and MS said somethings needed to be sorted. IW acknoledged this and worked out the issues in the background before submitting it back to MS. Meanwhile back at MS headquarters, someone pushed the button and released it onto the marketplace
Idiots. (This is according to a mate who works as a tester at EA in Madrid)
The update fixed the issues and I've been fine on it since the night it was launched.