"Undefined index: #type" on clean D6 install

I've set up a clean D6 install (current CVS branch) and added the current HEAD version of hierarchical select.
After enabling the "Hierarchical Select" module the following error message is displayed (142 times) on the admin/build/modules page:

notice: Undefined index: #type in /home/litrik/workspace/drupal-6/sites/all/modules/hierarchical_select/hierarchical_select.module on line 1426.

After I change line 1426 from

if ($form['#type'] == 'hierarchical_select') {

to

if (isset($form['#type']) && $form['#type'] == 'hierarchical_select') {

the error disappears.