When accessing Confluence 5.4 through a URL other than its configured base URL, the "files attached" icon on the main page view is still rendered using an absolute URL (based on the base) rather than a relative URL. In the situation where the base URL is inaccessible for whatever reason (proxy server issues or whatever), this yields a broken image icon. See the attached screenshot.

In this case, the specific IMG SRC for the icon is "http://localhost:8096/s/en_GB-1988229788/4726/ae47f2be84292af5a42aed58ebcd4cb49e436f6e.1/_/download/resources/com.atlassian.confluence.plugins.confluence-page-banner:page-banner-resources/images/grey_attach.png"

All of the other image assets on the page appear correctly.