I think you might have changed the synch mode (that's what the 1/48 is unless you change it). See if you can change the shutter speed in the synch mode menu and see if the new shutter speed shows up. (Note that when shutter is OFF it's 1/50...and my factory default for synchro was 1/48...but you can change it).
Are you in FILM CAM mode, or VIDEO CAM mode? If in FILM CAM, you won't see 1/48th, you'll see 180.0d (for 180 degrees). If you're in VIDEO CAM mode, it'll show up as 1/48th.
You find it below 1/24th and above 1/2000th; it's the shutter speed between where they wrap around from slowest to fastest.