What configuration would limit my DSLR's shutter speed to 1/200?
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 back 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.
+1 Just found out that the Nikon D3000 behaves the same though I cannot set it past 1/200 at all when flash is turned on unlike your T4i.
The camera is likely setting the shutter speed to match the flash sync speed of the camera. If it was set any faster, you would get black bands of underexposure across your shots, or at the fastest speeds a completely black shot. This is because the shutters would have finished moving to some degree before the flash completed its fire.