Hierarchical Select fails to update when the server doesn't support clean urls

I set up a fresh new drupal installation
- new database
- clean URLs disabled

Contrib modules:
- jquery_update
- jquery_interface
- hierarchical_select

i created a new content type:
- route

i created a new vocabulary "Region" (required, single Hierarchy, content type route):
Italy
--Subregion 1
----Sector 1
----Sector 2
----Sector 3
--Subregion 2
----Sector A
----Sector B
----Sector C
--Subregion 3
----Sector A
----Sector B
----Sector C

When i create a new route and select "Subregion 2" it showes me only the options for "Subregion 1" (Numbered sectors 1, 2, 3) and not the A, B, C