Haven't had any other reports like that. Did you try in live mode? That's where it would really count In live mode, you can cancel the payment within 15 minutes with no fee incurred. Please try that.
Do you have SSL setup on your site? It's required for Google Checkout to work correctly.
There are notes in the backend of DT Register that tell you how to set this up. It says:
Login to Google Checkout, go to the Settings tab, then click Integration to find the settings you need for DT Register, which are the Merchant ID and Merchant Key. In your Checkout integration settings, check the box for "My company will only post digitally signed carts." Then set the API Callback URL as
https://www.YOURSITE.com/components/com ... cation.php
. Note that this MUST be a secure https URL or it will not work. Then set Callback Contents to "Notification as HTML".
As you can see there... SSL is required for Google Checkout to work correctly.