When editing some pages the last changes have been lost

Hi XWiki users and developers, I have recently moved from Zope's zwiki to xwiki and I'm very impressed with it. My congratulations to the developers. Almost everything is working correctly, but there is one issue which is very annoying: For some pages when I click "Edit page" the content shown on the textarea is old! In fact it is the content I inserted the first time I edited it. If I insert new content it is shown when I finish editing, but when I edit it again it is lost. I have the feeling that it only happens with the pages I created just after installing Xwiki using the user Xwiki.Admin. I've searched in the documentation and list archive without luck. Can anyone help me with this problem? Cheers, Jorge PD: The details of my installation are: Xwiki v0.9.840 Apache Tomcat 4.1.31 Debian GNU/Linux 3.1 MySQL 4.0.24