When the protocol is entered wrongly (like http:/example.com, lacking one slash) IE7 will add the host name of the current site access to the URL. So when someone on the frontend clicks that link, they will be sent to the admin interface.

FF stores the link as it was entered (http:/example.com). The browser (FF at least) interprets such broken links as if they were relative (like /example.com, thus it gets expanded to http://mysite.com/example.com). This is maybe not perfect either, but quite acceptable IMHO.

Steps to reproduce

On a site with host based site access matching, open the admin interface in IE.

• create and article, enter some text using OE
• mark some text and open the insert link dialog
• enter a link with a broken protocol (like http:/example.com), press OK.
• store draft
• disable OE, check the source code for the link
  In FF3, the link is stored as it was entered. In IE7 (this is the bug) it is stored as http://myadminsite.com/example.com