user_access fails on custom actions

I'm having a problem where my custom actions produce this error message when my vbo page loaded:

Warning: Illegal offset type in isset or empty in user_access() (line 796 of /XXX/modules/user/user.module).

I tracked this down to line 230 of views_bulk_operations_handler_field_operations.inc:

        $perm = actions_permissions_get_perm($this->all_operations[$key]['label'], $this->all_operations[$key]['callback']);

actions_permissions_get_perm() returns an array, but user_access(), which is run several times on $perm, requires a string.