Starting a while ago with the svn version whenever a user selects the Advanced Skin under the Display Preferences all pages will display the following error:
SquirrelMail notice messages
Message: Undefined variable: message_list_href
As soon as switching back to the default skin the message disappears.
The odd thing is that the default skin also uses that variable in the file read_menubar_nav.tpl but it's not causing an error.
It seems that the variable is originally defined in src/read_body.php:
This is a default installation from svn without any plugins enabled. Tried it again with a checkout tonight, July 25th, 2007.