Hi Hans,
I'm currently testing 4.1.0p3 within Sage.
In debug mode, I still get:
ring r5 = (complex,15,j),(a,b,c),dp';
***dError: assume violation at numbers.cc:434 condition: n->cfCoeffName!=ndCoeffName
So I assume a simple fix as for other rings is needed here.
Best,
JPF