As the question implies, on occasion Drupal's log is showing that the favicon is not found. Indeed, it does not show in the browser tab or address bar. At other times, even within the same surfing session, it does show up.
Why does it do this and how can I prevent it so that the favicon will always show?
I am using version Drupal 7.22. with a custom subtheme and an admin theme (Stark).
My favicon is set in the subtheme theme configuration at sites/default/files/images/favicon.ico and that is located there as I have checked via FTP.
The log shows the browser is looking in example.com/favicon.ico.
The custom subtheme I use has
<link rel="shortcut icon" href="http://example.com/sites/default/files/images/favicon.ico"; type="image/vnd.microsoft.icon" /> in the source code and the admin theme (Stark) uses
<link type="image/vnd.microsoft.icon" href="http://example.com/misc/favicon.ico"; rel="shortcut icon"> and this file also exists in that location (not actually using example.com, of course).
Drupal is using clean URLs.
The web server is Apache on Debian Linux.