Testing equality for elements in a quotient of a multivariate polynomial ring

[Keir Lockridge]

I'm experiencing what seems to me to be inconsistent behavior in testing equality for elements of a quotient ring. In the code below, the first print statement gives "False", but the second one gives "True". Am I doing something wrong?

A = Integers(4)
R.<x,y> = PolynomialRing(A,2)
I = R.ideal(x^2 + 1, y^2 - 1, 2*x)
Q.<s,t> = R.quotient_ring(I)
T = s*t
U = -s*t
print T == U
print T - U == 0