Negative variable degrees, incorrectly computed Ext/Cohomology

[kschwede]

Hi all, when computing a certain Ext (a canonical module) of a homogenous equation with negative degrees, I get an unexpected zero.

i1 : S = QQ[X,T,Degrees=>{1,-1}]

o1 = S

o1 : PolynomialRing

i2 : Ext^1(S^1/ideal(X*T-1), S^1)

o2 = 0

o2 : S-module

This Ext should never be zero.

Note, if you set Degrees=>{1,-2} so it is not homogeneous, there is no problem (note, the answer should be S^1/ideal(X*T-1) up to some shift.

Doing it manually doesn't have a problem.

i1 : S = QQ[X,T,Degrees=>{1,-1}]

o1 = S

o1 : PolynomialRing

i2 : myRes = res(S^1/ideal(X*T-1))

      1      1
o2 = S  <-- S  <-- 0
                    
     0      1      2

o2 : ChainComplex

i3 : myResDual = Hom(myRes, S^1)

             1      1
o3 = 0  <-- S  <-- S
                    
     -2     -1     0

o3 : ChainComplex

i4 : HH^1(myResDual)

o4 = cokernel | XT-1 |

                            1
o4 : S-module, quotient of S

That is, I get the right answer.