Fatal error: Cannot redeclare _phptemplate_variables()

Hi,

I've set this as a "bug" but am not sure if it's a code or configuration issue. In any case, I'm getting the following error when I access my site as anonymous (having set the authenticated theme to Garland, and the anonymous theme to Zen):

Fatal error: Cannot redeclare _phptemplate_variables() (previously declared in /Users/aeropine/drupal/themes/garland/template.php:58) in /Users/aeropine/drupal/sites/all/themes/zen/template.php on line 59

It seems as though the garland theme's declaration needs to "go away"/descope in order for the zen one to work...

Am I doing something wrong? Any help appreciated.

Thanks.