Calling non-existant admin_drilldown_menu_tree_output theme callback

After a recent update to 2.0 I started getting this error message:

Warning: call_user_func_array() [<a href='function.call-user-func-array'>function.call-user-func-array</a>]: First argument is expected to be a valid callback, 'theme_admin_drilldown_menu_tree_output' was given in theme() (line 660 of /project/includes/theme.inc).

I traced it down to line 72 in admin.module, where it tries building the "create block" using theme('admin_drilldown_menu_tree_output', ...). This theme callback doesn't exist. Maybe this is related to #877996: Admin redeclares admin_menu's theme_admin_menu_item()? That patch seems to be only half-way applied?

When I manually applied the part for theme/theme.inc, then it worked as expected again. Somehow that last part of the patch was left out.