pdim is inconsistent

In the following example, I give two generating sets for the same module, and pdim gives a different answer for each.

i1 : R = QQ[x,y];
A = matrix {{-2*y+1, x^2+y^2-y, 2*x*y-x}, {2*x, 0, 2*y^2-2*y}};
B = matrix {{2*x*y-x, 4*x^2-1}, {2*y^2-2*y, 4*x*y-2*x}};

             2       3
o2 : Matrix R  <--- R

             2       2
o3 : Matrix R  <--- R

i4 : imA = image A

o4 = image | -2y+1 x2+y2-y 2xy-x  |
           | 2x    0       2y2-2y |

                             2
o4 : R-module, submodule of R

i5 : imB = image B

o5 = image | 2xy-x  4x2-1  |
           | 2y2-2y 4xy-2x |

                             2
o5 : R-module, submodule of R

i6 : imA == imB

o6 = true

i7 : pdim imA

o7 = 1

i8 : pdim imB

o8 = 0

Reproduce the reported QQ[x,y] example in Macaulay2, starting with the image and pdim entry points and checking that imA == imB. Compare the two pdim results and identify the responsible computation; done means equivalent generating sets receive the same projective dimension.