Backlash problem?

I have a converted mini mill (yes, I know). When I run a program
which jogs the y axis back and forth 20 times with my current
backlash setting (in Mach2 v6.06) I get a perfect reading
(within .0005). When I run the following program, I get a +.033 creep
in the Y axis for every complete circle:

G0 G49 G40 G17 G80 G50 G90
M6 T1(TOOL DIA. 0.5625)
G64
G20 (Inch)
M04 S0
G00 G43 H1 Z0.1
X0 Y0
G01 Z-0.0010 F15
G2 Y0 X0.4500 R0.2250 F15
Y0 X-0.4500 R0.4500
Y0 X0.46875 R0.46
Y0 X-0.46875 R0.46875
X0.46875 Y0 R0.46875
Y-0.375 X0.09375 R0.375
G00 Z0.1
X0 Y0
...

The control response to this code correctly (it actually generated
this code with its wizard) by cutting a circular pocket (Z is then
decremented and the code is repeated) but it slowly moves +.033 on
the Y axis on every iteration.

I have changed the feed to 1,5,10 and the motor tuning acceleration
and speed to a low and high settings to no avail.

I assume a small calculation round off error but not .033/circle.

Any help would be appreciated.