Header_bg gone in IE6 but ok in Firefox!

Hello.

Something very strange (to my very limited understanding of css/html) in our soon-to-go-live store. We've modified /includes/templates
/classic/images/ header_bg.gif to get some idea on simple template editing. We then tested the results in both IE6 and Firefox. Seeing it was ok we continued our other php/Admin based work using Firefox.

Now we're facing this: we open the store in Firefox and the header_bg appears fine. We open it with IE6 and header_bg is gone while something like a second row of tile_bg appears.

How can this be explained? It's not an issue with the browser's cache fouling things up.

(I've attached two screenshots that show this weird problem)

Any thoughts very much appreciated

You should have used the template_default as a roadmap,
the classic template was only included as a backwards compatible demo for folks upgrading from 1.2 to 1.3

renamed the archived original tile_back and header_bg to their initial names (in the classic template). got the old brown look but the problem persists in IE6.

Did you ever get this sorted?