Update: This workaround is only needed if you use "folders" in the image resource name.
If you have multiple local stylesheets on a page, the CSS files are combined into a single file.
This changes the url to the stylesheet (adds xsp/.ibmmodres/.css after the path to the db).
If you have an image reference like url(image.png), the image can no longer be loaded, as the url is relative to the path of the stylesheet.
To work around this issue, add ../../../ to the image reference.