I'm using a T4i with a 100mm f/2.8L (with macro twin flash). In manual mode, I could select any shutter speed down to 1/4000. However, when shooting the DSLR would set it bacback to 1/200. Does it depend on some configuration parameters I did not check/uncheck or upon the flash speed? I'm sure I remember shooting at higher shutter speeds, perhaps with other lenses, if I'm not mistaken.