In Sharon Tube Company v. Workers' Compensation Appeal Board (Buzard), 908 A.2d 929 (Pa. Cmwlth. 2006), the claimant, who had returned to work with a loss of earnings as of July 21, 2003, again stopped working. The employer and the claimant then executed a supplemental agreement, specifying that the claimant was totally disabled as a result of his work injury as of July 28, 2003. Thereafter, the employer filed a petition to modify the claimant's benefits as of July 21, 2003, alleging that the claimant had some earning capacity. The Court held that the employer's execution of the supplemental agreement reflected the employer's acknowledgement that claimant's total disability had recurred. The Court rejected the employer's more limited characterization of the supplemental agreement, i.e., that it showed only that the claimant had stopped working. Stated otherwise, a supplemental agreement may not be modified retroactively. To have benefits modified pursuant to Section 413 of the Act, 77 P.S. 772, an employer must prove that a claimant's condition has changed since the date of the supplemental agreement.