multivar polynomials over poly fraction fields don't simplify

[rwst]

sage: F=FractionField(PolynomialRing(QQ,'t'))
sage: R=PolynomialRing(F,'x,y')
sage: R.inject_variables() 
Defining x, y
sage: x/x 
x/x

whereas simpler fraction fields for F yield 1

CC: @sagetrac-jakobkroeker

Component: commutative algebra

Issue created by migration from https://trac.sagemath.org/ticket/15971

[sagetrac-jakobkroeker]

comment:3

Seems fixed now. Needs a test, then review