Steps To Reproduce

sage: from sage.rings.polynomial.multi_polynomial_sequence import PolynomialSequence
sage: R.<x,y> = QQ[]
sage: PolynomialSequence([x+2*y+3, 4*x, 5]).coefficient_matrix()
(
[1 2 3]  [x]
[4 0 0]  [y]
[0 0 5], [1]
)
sage: _[1].parent()
Full MatrixSpace of 3 by 1 dense matrices over Multivariate Polynomial Ring in x, y over Rational Field

Expected Behavior

The second element should be a vector - it is the vector of monomials appearing in the sequence.

Actual Behavior

It returns a 1-column matrix.

Additional Information

The problem is that iterating over a vector gives the elements, whereas iterating over a 1-column matrix gives vectors.

Environment

irrelevant.

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide