Distance sorting takes no effect.

[pasine]

I've noticed that:

@nearest_pois = Poi.within(radius, :units => :km, :origin => [lat,lng], :order => 'distance ASC').limit(limit)

and

@nearest_pois = Poi.within(radius, :units => :km, :origin => [lat,lng], :order => 'distance DESC').limit(limit)

gives the same result.
It's like sorting has no effect.
This is my Poi configuration:
acts_as_mappable :default_units => :kms,
:default_formula => :sphere,
:distance_field_name => :distance,
:lat_column_name => :lat,
:lng_column_name => :lng

Is there something wrong?