reference map size

[Peter Drake]

I am having a problem getting the reference map size to accept changes
via parameters in a URL as described here:
http://mapserver.gis.umn.edu/doc40/cgi-reference.html#mapfileURL

The parameter "map_scalebar_size=100+5" gives me a scalebar 100px X
5px.  The paramter "map_reference_size=60+40" does not give me a
reference map of size 60px X 40px as I would expect.  Instead, it
gives me a reference map of whatever size is defined in the .map file.
 Am I doing something wrong?  Can anyone confirm if this is a bug?
Thanks!