Can't add a ".ico" favicon

Steps to reproduce:

1. Log in as admin
2. Go to the administration page, up to main menu bar: "Wiki" -> "Administer Wiki"
3. Click on "Presentation" under "Look and Feel"
4. Press the "Customize" button on top of Skin (XWiki.DefaultSkin)
5. Scroll down and press the "Cancel" button to exit the edit view (as we only need to add attachments)
6. Click on "Attachments"
7. Attach a favicon with the following name: "icons.xwiki.favicon.ico" (for the "traditional" favicon)
8. Refresh the page

Expected results: The icon next to the URL in the browser bar is changed to the new icon attached.

Actual results: The icon doesn't change.

Note: I've also tried with the png version (icons.xwiki.favicon16.png - for a small (16x16px) version of the favicon in PNG format), and that works - http://www.xwiki.org/xwiki/bin/view/FAQ/How+do+I+add+a+favicon+for+my+wiki