Indeed, forward funding is a violation of the time statute in which you are obligating in advance of need. The Bona Fide need rule comes into question.
In addition, expired funds cannot be used for any new work or obligations efforts; but are acceptable to use to modify existing contract vehicles.
Please keep in mind that this response is from a Department of Defense point of view, and may be different than your agency. Please contact your local comptroller and fiscal law attorney for further guidance.