This bug does not exist in 1.2.0, although the error message could be better worded to say "X is a macro"

(setf (fdefinition 'x) (fdefinition 'f1))                                                                                                                                     
(setf (macro-function 'x) (macro-function 'm1))                                                                                                                               
(funcall 'x)

debugger invoked on a UNDEFINED-FUNCTION in thread
#<THREAD "main thread" RUNNING {1002C468A3}>:
  The function COMMON-LISP-USER::X is undefined.