If the line: %undefine _fixgroup is in a spec file, it undefines other macros (at least %_gzipbin), even if the %undefine line is commented out. The only way to avoid this is to remove the line from the spec file.
BTW: rpm 3.0 will expand macros even in comment lines. The symbol hash table was truncated by the deletion of %_fixgroup. Fixed in rpm-3.0.2-0.8.