I'm not familiar with all trans brake valve bodies but I'm fairly certain that they all apply the front clutch as the locking member. When the car is staged and the shifter is in low, (LBA apply in this case) the rear clutch is on as well as the rear band. When the trans brake is applied it engages the front clutch which locks the whole trans up. When the button is released, the front clutch releases and you launch in low. In high gear, the front clutch is applied as well as the rear clutch, so engaging the t-brake button in high should do nothing as the front clutch is already on. I would look in the rear servo area for an issue. If the rear band applied in high, this would lock the trans up and the band and drum are pretty beat up by the pictures.