When the content of a menu item is edit, the menu item desapear

This is a weird bug on drupal menu system.
I have a site updated from drupal 6.20 to 7.rc3.
Now, when i edit a node that have a menu item, the menu item is deleted, it is not any more on menu, but i just edit the node content, nothing on menu part, so everytime i change the content of node, i have to recreate the item on menu.