module filters: bug in search results

I have a module filters

with filters generated by a multilevelselect field

the serach results generated by this module are ok if I am visiting the main section,

but instead if I am visiting one of the subcategories

then there are no search results

in case I choose filters which are assigned to records which are in a different category

if you test you may understand better

http://www.sarteanoliving.it/it/turismo

this is the main section page, here search results are always ok

http://www.sarteanoliving.it/it/turismo/categoria/2-sarteano/52-mangio

this is category "mangio" page, here if you use the filter module on the left and choose the first filter "per dormire (36)"

then you get no results

this happens because the records assigned to "per dormire" filter are in a different category, not in "mangio" category

I think this should not happen, as it compromise very much the usability of the filter module