Array to string conversion (when used with search_api and hierarchical_select)

I'm getting the following errors when using hierarchical select in conjunction with search_api and global filter:

• Notice: Array to string conversion in _hierarchical_select_process_calculate_selections() (line 1185 of ...\sites\all\modules\contrib\hierarchical_select\hierarchical_select.module).
• Notice: Array to string conversion in _hierarchical_select_process_calculate_selections() (line 1185 of ...\sites\all\modules\contrib\hierarchical_select\hierarchical_select.module).
• Warning: Illegal offset type in isset or empty in taxonomy_get_children() (line 1076 of ...\modules\taxonomy\taxonomy.module).
• Warning: Illegal offset type in taxonomy_get_children() (line 1088 of ...\modules\taxonomy\taxonomy.module).
• Warning: Illegal offset type in isset or empty in taxonomy_get_children() (line 1091 of ...\modules\taxonomy\taxonomy.module).

It seems that by using global filter the underlying function "_hierarchical_select_process_calculate_selections()" is called and doesn't receive a flat list of id's in its array but rather the hsid and the lists of id's in a sub array. See debug screenshot.

Global filter should not send the hsid to the contextual filter. I don't really have a lot of knowledge on this module so I hope the maintainer can propose a solution for this.