How should polynomials be defined in a given polynomial ring?

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Using SageMath 10.5, if I enter

R.<x,y>=PolynomialRing(QQ); f(x,y)=x+y; f in R

I would expect "f in R" to return either True or False. Instead it gives me a runtime error (message copied below). Is there a fix or workaround for this?

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-3-b05dc0c8ff91> in <module>
----> 1 f in R

/usr/lib/python3/dist-packages/sage/structure/parent.pyx in sage.structure.parent.Parent.__contains__ (build/cythonized/sage/structure/parent.c:10491)()
   1162         try:
   1163             x2 = self(x)
-> 1164             EQ = (x2 == x)
   1165             if EQ is True:
   1166                 return True

/usr/lib/python3/dist-packages/sage/structure/element.pyx in sage.structure.element.Element.__richcmp__ (build/cythonized/sage/structure/element.c:10491)()
   1110             return (<Element>self)._richcmp_(other, op)
   1111         else:
-> 1112             return coercion_model.richcmp(self, other, op)
   1113
   1114     cpdef _richcmp_(left, right, int op):

/usr/lib/python3/dist-packages/sage/structure/coerce.pyx in sage.structure.coerce.CoercionModel.richcmp (build/cythonized/sage/structure/coerce.c:20582)()
   1971         # Coerce to a common parent
   1972         try:
-> 1973             x, y = self.canonical_coercion(x, y)
   1974         except (TypeError, NotImplementedError):
   1975             pass

/usr/lib/python3/dist-packages/sage/structure/coerce.pyx in sage.structure.coerce.CoercionModel.canonical_coercion (build/cythonized/sage/structure/coerce.c:12602)()
   1330                 if x_elt._parent is y_elt._parent:
   1331                     return x_elt,y_elt
-> 1332             self._coercion_error(x, x_map, x_elt, y, y_map, y_elt)
   1333
   1334         cdef bint x_numeric = isinstance(x, (int, long, float, complex))

/usr/lib/python3/dist-packages/sage/structure/coerce.pyx in sage.structure.coerce.CoercionModel._coercion_error (build/cythonized/sage/structure/coerce.c:21337)()
   2029             <class 'str'> 'g'
   2030         """
-> 2031         raise RuntimeError("""There is a bug in the coercion code in Sage.
   2032 Both x (=%r) and y (=%r) are supposed to have identical parents but they don't.
   2033 In fact, x has parent '%s'

RuntimeError: There is a bug in the coercion code in Sage.
Both x (=x + y) and y (=(x, y) |--> x + y) are supposed to have identical parents but they don't.
In fact, x has parent 'Symbolic Ring'
whereas y has parent 'Callable function ring with arguments (x, y)'
Original elements x + y (parent Multivariate Polynomial Ring in x, y over Rational Field) and (x, y) |--> x + y (parent Callable function ring with arguments (x, y)) and maps
<class 'sage.structure.coerce_maps.DefaultConvertMap_unique'> (map internal to coercion system -- copy before use)
Coercion map:
  From: Multivariate Polynomial Ring in x, y over Rational Field
  To:   Callable function ring with arguments (x, y)
<class 'NoneType'> None