Panel page content not editable

Strange bug that happened to me several times.

Sometimes a panel page is "blocked", i mean i can't edit its content anymore, details here :
- I edit my custom content, in the popup window, then Save, then i do save on the panel page content edit form => i check again the content in the popup, the modification disappeared
- Same if i add a new block of content, after a save in the form, the new block is not there
- There is no js error
- The same bug with firefox or chrome, that means browser independant
- Other tabs in the panel conf (parameters/layout etc..) are still editable
- No cache enabled, Panels simple cache module not enabled
- Tested after a clear cache in /admin/settings/performance
- Some other panel page content is still editable at the same time
- No errors in httpd logs
- One classical error in /admin/reports/dblog: "The specialized Panels menu router rebuild failed. ..."
- Bug is the same under 6.x-2.0-alpha2 and 6.x-2.x-dev 2008-Nov-21
- Tried a cron tab before editing
- I even tried to add a new panel page with the same content, i can edit if, when i delete the old one and set the new one with the former url, it is blocked again
- I suppose this is a trouble with the ajax http://www.mydomain.com/panels/ajax/configure/18/54

Phil