Edit a page in the 'Rich Text' tab. Press '[', select 'Insert Web Link' and enter any URL/Link Text and click 'Insert'. Now attempt to save the page. This results in the following error,

The following error(s) occurred:
An error occured while trying to save the requested page.

Looking at the wiki markup, this occurs because of an erroneous <feff> entity prefixed to the link. When copied into a basic text editor (e.g. vim) it looks like,

<feff>[test|http://bbc.co.uk]

Removing this erroneous character allow the page to be saved.

This behaviour affects,
Mac 10.6.6/Chrome 8
Mac 10.6.6/Firefox 3.6
Windows XP/Firefox 3.6
Windows XP/IE8