scalebar units

[Stéphane RIFF]

I want to change scalebar units via phpmapscript when scale under a
certain number.
I want to change from MS_KILOMETERS to MS_METERS.
I did it like this :
  $map->scalebar->set("units",MS_METERS);

This seems to work because when i look in the mapfile after
$map->save(<filename>)
I see UNITS METERS in the scalebar section. The problem
is when i reload the .map file i've just save and draw an image from it
the scale is still in KILOMETERS........

Does someone success in changing scalebar units with phpmapscript ???
Thanks