Matrix ordering being mistaken as non-global

[ren]

I'm currently doing some tropical computations with zero-dimensional ideals in which I need to apply some unimodular transformations (i.e., morphisms which operate on the exponent vectors via a non-negative unimodular map). I can speed the process up by also changing the ordering so that a Groebner basis is mapped to a Groebner basis, but Singular seems to mistakes some Matrix ordering as non-global:

> intmat M[2][2] = 1,0,-3,1;
> ring r = 0,(x,y),M(M);
> basering;
// coefficients: QQ
// number of vars : 2
//        block   1 : ordering M
//                  : names    x y
//                  : weights  1 0
//                  : weights  -3 1
//        block   2 : ordering C
> x+1; // x>1
x+1
> y+1; // y>1
y+1
> ideal I = x,y;
> option(redSB);
> I = std(I);
> ring s = 0,(x,y),lp;
> fglm(r,I);
   ? only works for global orderings
   ? ring r and current ring are incompatible
   ? error occurred in or before STDIN line 10: `fglm(r,I);`