Fanuc 21it lathe workshift problem

Hi all, Im relatively new to CNC so I could be making an obvious mistake here!
I have a Fanuc controlled Harrison 330 Alpha lathe, its a great machine being very versitile but Im having trouble with setting the Z workshift in full CNC mode. There is no G54 active on this machine.
To set the workshift I call up the first tool T0101 in mdi and the set the position I want Z 0 with that tool, I then go to workshift and input Z0, when I then command T0101 Z 0 in mdi the postion of the tool goes to Z -33.295 which happens to be the offset of tool 1, consequently if I then repeat the process of setting the workshift as before it works fine and goes to the correct tool 1 Z 0 position!, and will from there on unless the computer is restarted! Obviously this will cause a crash if I run a program. I could/ very likely be doing something wrong procedurely or possibility setting tooloffsets incorrectly. Id post some pictures of the screen but not sure how to.
Any guidance appreciated on what the problem might be.