Hi,
yes that would tend to indicate that Mach is causing the X and Y axes move together.
Try MDIing some separate X and Y moves:
G0 X50
X0
Y50
Y0
That should move X 50mm then back again, then Y 50mm and back again. Does it do that or do both axes move together?
When the axes move together do both the X&Y DROs change together?
Does your friend have his machine set up and running?
Craig