CiviCRM ACL Cache does not get truncated on group

(from an email sent by dgg which i was able to reproduce)

I created Volunteer role which does NOT have edit contact permission.
Assigned that to volunteer / volunteer user.
So far so good - they can only view contacts

Then I added Jane Volunteer to the Administrators group (which has the
Admin ACL Role which has Edit for All Groups).
Now she can edit contacts - still good.

Then I removed Jane Volunteer from Administrators group

• • • Now she can STILL edit contacts:
      http://drupal.demo.civicrm.org/civicrm/contact/view?reset=1&cid=77

-.....

Not sure if related - but getting this error now on Manage Groups when
logged in as volunteer / volunteer
(http://drupal.demo.civicrm.org/civicrm/group?reset=1)
warning: in_array() [function.in-array]: Wrong datatype for second
argument in /var/www/drupal.civicrm.org/public/sites/drupal.demo.civicrm.org/modules/civicrm/CRM/ACL/API.php
on line 147.