"hidden" Filter is still visible in advanced search

I have set ne of my fields as follow

filter enable - yes

filter hidden - yes

but as you can see here http://agrietour.eu/NEW/fattorie

the filetr si still visible in advanced search

it is the last one "Rivolta a"

for what I see the filter label is visible in advanced search, but if I click it the filter selct box is not beng loaded, it just display the boolean tool, which is for the first filter in the row, not for this last one

so it seems that in my case hiding the filter, hides the selectbox, but not the filter label

also notice that this field is part of a group of fields, I don't know if this can cause this kind of issues