[KevinH]

Tried your updated bug epub and the url is properly updated.
That said, your css is simply wrong:

Pseudo-Elements are done as follows:

selector::pseudo-element {
    property:value;
}

Note the double colons before the pseudo-element.

Also the pseudo-element "::before" does not exist or validate in CSS 2.1 but does validate for epub3.

Also as anything *before* the initial heading element in your example has no vertical size, no background image is displayed (as the image height would be 0).

So changing that css to something along these lines is what I think you want:

h1::before {
    content: url('../Images/gold-aureus.jpg');
    display: block;
}

This shows the image you want nicely before every h1 in the document.

So there is no bug here that I can see.

KevinH