Query problem with two sets of checkboxes & reducing duplicates

I'm using this module (ported to 6.x) to expose 2 sets of checkboxes (based on different vocabularies) alongside an exposed search box. Things go pear-shaped when one of the sets of checkboxes is left blank. The last part of the query illustrates this. It queries the blank one as zero so I always get no results back. WHERE (term_node.tid IN (104, 0, 0, 0, 0, 0)) AND (term_node2.tid IN (0, 0, 0, 0, 0, 0, 0)) AND (term_node3.tid = 44)

Here is the same part of the query when it works (both sets of checkboxes are checked.): WHERE (term_node.tid IN (104, 0, 0, 0, 0, 0)) AND (term_node2.tid IN (41, 0, 0, 0, 0, 0, 0)) AND (term_node3.tid = 44)

Can someone point me in the direction of how to fix this? I tried to use just one set of checkboxes alongside a Views multiple-select list, and I still get the same issue.

Also, the option to reduce duplicates doesn't seem to work using this module. Does anyone know how to implement this? Thanks!