Zen subthemes need node.tpl.php

Despite having used Drupal for more than a year and a half I still feel like a novice.

I was using Zen 6.x-1.0 and decided to upgrade to Zen 6.x-1.1 and I am not sure if the same thing applied before with version 1.0 since I've made changes while sorting this out.

Components:
zen 6.x-1.1
OG 2.0

I have a subtheme with node-og-group-post.tpl.php copied from the og/theme directory and it is modified. However, the changes are not effective, even after empty caches.

If I copy the node.tpl.php file from the zen/zen directory to the subtheme everything works fine and the og posts display as expected. Even if I do not need to modify the node.tpl.php file.

I have confirmed that the same thing happens when I use the zen classic subtheme. The og tpl.php files are not active until the default node.tpl.php file is copied into the zen classic subtheme folder.

I did not think this was necessary and thought the subtheme would be aware of the default file residing in the zen theme itself. There is no mention in the readme of the need to copy this file to the subtheme.

I am not sure if I am misunderstanding something, or doing something wrong, or if this is a bug. I'd appreciate hearing what others think. Thanks,

Izzy