wp_remove_object_terms() Returning false despite proper use?

Very odd problem.

wp_remove_object_terms() is returning false, despite proper use.
( http://codex.ww.wp.xz.cn/Function_Reference/wp_remove_object_terms )

Is there anything strange or buggy concerning this function? I see very little mention of it online…

Using WP 3.8

case 3:

    	ss_categories_dropdown( $dropdown_id , 0 , $tax );

    	$ids = explode( ',' , $_POST[ 'ids' ] );
    	$cat = $_POST['cat'];

    	if ( $tax == 'image-type' )
    	{

    		foreach($ids as $id){

    			wp_remove_object_terms( $id, $cat, $tax );

    		}

    	}

    	echo '<p class="description">Category "' . $term->name
    	. '" removed from selected images.</p>';

    	break;