This macro doesn't appear to function the same as the built-in G90. With external G90 macro enabled, X motion is 1/2 what is specified. For example, run this program with the external G90 enabled:
G00 X1.0 Z0.0
G90 X0.5 Z1.0
Select the plot line produced by the G90 and it's location is:
Line at Feed
Tool 0
Start Z0.0 X0.25
End Z1.0 X0.25
Length 1.0
Delta Z 1.0
Delta X 0.0