Custom error breaks theme switching modules such as Theme Key: http://drupal.org/project/themekey Taxonomy Theme : http://drupal.org/project/taxonomy_theme Section: http://drupal.org/project/sections and SwitchTheme: http://drupal.org/project/switchtheme
According to this: http://drupal.org/node/594484 it's more of a Drupal 5/6 core bug but it is possible to avoid.
Comments
Comment #1
gisleDrupal 5 is no longer supported and this will not be fixed. If you're on D5 and perceive this as a problem, use workaround suggested by OP.