If one takes a modsym with coefficients in a nontrivial extension of QQ and a nontrivial character, and then applies "completions", the completed modsyms have values in a new p-adic field but their characters have values in the old field, and this leads to coercion errors.
Test case:
sage: f = Newforms(Gamma1(13), names='a')[0]
sage: phi = f.PS_modular_symbol()
sage: phi3 = phi.completions(3,8)[0]
sage: phi3.hecke(7)
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TypeError Traceback (most recent call last)
[...]
TypeError: unsupported operand parent(s) for '*': 'Full MatrixSpace of 1 by 1 dense matrices over Eisenstein Extension of 3-adic Field with capped relative precision 8 in a defined by (1 + O(3^8))*x^2 + (3 + O(3^9))*x + (3 + O(3^9))' and 'Number Field in alpha with defining polynomial x^2 + 3*x + 3'
If one takes a modsym with coefficients in a nontrivial extension of QQ and a nontrivial character, and then applies "completions", the completed modsyms have values in a new p-adic field but their characters have values in the old field, and this leads to coercion errors.
Test case: