On the "Offsets" screen, there are coordinates for "Current Work Offset" and "Machine Coordinates". If the values on either coordinates are not "0", trying to set the values to "0" on one set of coordinates causes the values on other set of coordinates to change. For example, the values of "Machine Coordinates" are 0,1,2 and the values of "Current Work Offset" are 0,0,0. Trying to change the values of "Machine Coordinates" to 0,0,0 causes the values 0,1,2 to appear in the "Current Work Offset" coordinates. Any suggestions?

You can only set the machine coords when you reference your machine, they are not user settable. The reason for this is they are the coords that Mach uses to keep a track of where it is.
Hood