phptemplate_block($block) in template.php returns invalid argument

exactly as noted in the readme, i have added the following code to my theme's template.php file:

function q1000a_block($block) {
  if (module_exists('blocktheme')) {
    if ( $custom_theme = blocktheme_get_theme($block) ) {
      return _phptemplate_callback($custom_theme,array('block' => $block));
    }
  }

  return phptemplate_block($block);
}

for quite a while when i go to my manage blocks page i have been plagued by the following error: "warning: Invalid argument supplied for foreach() in /path/to/drupal/modules/block/block.module on line 161."

after a good deal of detective work, i think i've discovered that returning phptemplate_block($block); may be the culprit. if i remove it, then there is no error (although none of the non-blockthemed blocks are displayed either). i have checked and there are no other callbacks to phptemplate_block in the template.php file.

has anyone else run into trouble with this? is there any way to fix this error?

thanks for looking into this problem.