LaurentPolynomial can't factor constants

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Hi all,

Many LaurentPolynomials throw errors when I try to factor them. For example:

sage: R.<x,y> = LaurentPolynomialRing(QQ)
sage: R.one().factor()
AttributeError: ...
sage: (x^-1).factor()
AttributeError: ...

This seems to come from the unit part of Polynomial.factor() sometimes (incorrectly) living in Integer Ring, and sometimes (correctly) living in whatever self.parent() is.

Is this intentional or a bug?

Thanks,

Henry