I spotted this while working on #12662:

QQbar(sqrt(2)) + QQbar(zeta(7))

will return a massive traceback concluding in

RuntimeError: maximum recursion depth exceeded while calling a Python object
sage: 

Component: algebra

Author: Mike Hansen

Reviewer: David Loeffler

Merged: sage-5.0.beta11

Issue created by migration from https://trac.sagemath.org/ticket/12665