I've erroneusly used the substitution $(....) in a rule in the style file lines as follow:

highway=* & route=* {set route_ref='$(route_ref), ${ref}' | '${ref}'}

and mkgmap don't return with some error or warning.

This substitution $(....), as state the manual, are reserved for the use in a apply rule in the relations file and are not usable in other style files.

I've found a mkgmap bug or what other?

Ataro