Selling the property purchased with a VA loan releases you from obligation to the VA loan. In the case of a loan assumption, however, this is not automatic. The borrower must notify either the VA or the lender and request that liability be transferred to the new owner. The borrower needs to request a "release from liability" notice from the VA.
There is an exception to this policy for those with loans closed before March 1, 1988. In these cases no notification is required, but it is a very good idea to request a release from liability from the VA anyway.