No problem with Qt 4.5.2 - haven't tested 4.5.3
Problem with 4.6.x as well as the 4.7 preview

I have an HTML document that looks like,

<img src="mydata://image_1" />
<img src="mydata://image_2" />
<img src="mydata://image_3" />

I then load it into QTextDocument for printing, and assign images as,

doc.addResource( QTextDocument::ImageResource, QUrl( "mydata://image_1" ), img1 );
doc.addResource( QTextDocument::ImageResource, QUrl( "mydata://image_2" ), img2 );
doc.addResource( QTextDocument::ImageResource, QUrl( "mydata://image_3" ), img3 );

then the latest image is used for all images.

If img1 and img2 is null and img3 is not null, img3 will appear in all placeholders in the document.
If I move addResource call to prior to img1, then img2 (last addREsource) will overwrite all images.

Edit: QUrl is the issue.