Proposed resolution (approved by CWG 2023-04-28):
Change in 7.6.1.9 [expr.static.cast] paragraph 2 as follows:
An lvalue of type “cv1 B”, where B is a class type, can be cast to type “reference to cv2 D”, where D is a complete class derived (11.7 [class.derived]) from B, if cv2 is the same cv-qualification as, or greater cv-qualification than, cv1. ...