I've been working on an email template and stumbled across something a bit odd. I'm using the bulletproof background images from Campaign Monitor http://backgrounds.cm/ and started to work on a header for it when I noticed that in Outlook 2007 and 2010 the background image doesn't render fully like this:

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When I view it in other clients its fine (eg Outlook 2011, Gmail, Mail, Thunderbird etc...).

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(BTW this isn't the final resting place for the logo, just what I sent for testing the background image was working ok.

Now if I add anything else at all to the <div> that the image is in then all of a sudden everything else appears.

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Has anyone else seen this before? I could drop in a non breaking space and it would work but I'm not overly happy on relying on that. By the time I've finish working on the design I will most likely have other things in the header (other logos or a menu) but I want to understand whats happening.

Any ideas whats happening would be great. Thanks.