I've had more than a few situations where the author does release the code...and it doesn't match the paper. The equations are different, restrictions are tight

I've had more than a few situations where the author does release the code...and it doesn't match the paper. The equations are different, restrictions are tighter, etc. It's the single most frustrating aspect of my job (excepting autotools). Releasing the code is another way that people can attack your conclusions, so maybe people are reluctant to do it?