That should not happen.
Did it always do that or has it just started doing it?
There are no common parameters for that but perhaps you are missing an option parameter(such as Direct Input Measurement or Workshifts G54-G59)
Try inputting a number on the SHIFT VALUE instead.
It sounds like you have the crappy workshift option like 0-T without proper workshifts (G54-G59).
Can you post a pic of your workshift screen here, maybe there is something else missing.
If all else fails you can use G50 X..... Z...... in the program.