-> calculation of disabilitation info (to write the set of $mform->disabledIf()) was using two query per loop and not only one
-> calculation of disabilitation info (to write the set of $mform->disabledIf()) was buggy for chain of conditioned items (item 3 dependes from the answer to item 2 that dependes from answer to item 1)
-> userform_get_parent_disabilitation_info was buggy for checkboxes
-> routine to assign items per pages was not considering hidden items