in latest firmware there is a update to S1Boot (to Version R10A21). I think most users who DONT USE PCC/SEUS will not have the update because Flashtool does not decrypt it correctly.
I packed it up into German Firmware, so if you are interested you can flash this Firmware and then just reflash ANY OTHER Firmware if you dont want to stay on German one. After S1Boot got updated it will stay updated no matter what Firmware you flash afterwards, becasue normally it is not included.
File can be downloaded here from my Firmware collection, directlink to Xperia T folder: