A Drilling Contractor in the Gulf of Mexico reports that subsequent to cementing surface casing using a jack up MODU, annular flow was reported to rig management. The integral diverter system that had been installed on the rig was placed in the “test” mode and the well was shut in to give time for the cement to set up. (The “test” mode is normally used to test the diverter system, after installation, in accordance with MMS requirements.) When pressures rose, the diverter flow line seals started leaking gas to the rig floor. Personnel evacuated the area and an attempt was made to divert the well from the remote station. Due to the configuration of the control system placed previously in the “test” mode on the rig floor, the remote would not operate the desired diverter functions. There were no injuries or environmental impacts due to this incident, however there were high potential consequences.