I think that the image that follows best describes the problem that I'm experiencing. It seems that for certain file types the associated icon in a package is being applied but with an overlay of the default icon registered with Windows. As you can see in the example, the icon for *.txt files is correct, and the icon for default (unknown/unassociated) files is also correct, but it has a 16x16 Internet Explorer icon on top of it. This also happens with other file types such as *.rar, *.jpg etc., depending on the icon package.

Is there a way to make sure that ONLY the package's icons get used without this overlay?