When making availability report using Host mode and filtering by specific host group, query is selecting all nested Host groups that has nothing to do with filtered one.

Example scenario:
Create Host group - Test group ( with host "1" inside it )
Create Host group - Nested/nested1 ( with host "2" inside it )
Create Host group - 1_Nested/1_nested1 ( with host "3" inside it )

Open Reports -> Availability report page.
Query from debug:

SQL (0.000292): SELECT g.groupid,g.name FROM groups g WHERE (g.name IN ('Nested','Nested/1_Nested'))
report2.php:434 ? CFrontendApiWrapper->get() ? CApiWrapper->__call() ? CFrontendApiWrapper->callMethod() ? CApiWrapper->callMethod() ? CFrontendApiWrapper->callClientMethod() ? CLocalApiClient->callMethod() ? call_user_func_array() ? CHostGroup->get() ? DBselect() in include/classes/api/services/CHostGroup.php:318