When adding a field to a content type, it is tempting to create a new field, and to assign it a name so unique that it could never possibly clash with the names of fields you may create in the future (at least in that particular Drupal installation). After all, most if not all Drupal developers have examined the field tables and columns in a Drupal database — in an attempt to determine everywhere that the field data is stored, and anything else in the database that can affect it — but have been frustrated when field names are similar enough to be confusing.

With the introduction of Drupal 7, developers may encounter a puzzling problem involving custom menus: imagine that you have created a custom menu — such as a list of secondary links for the footer of a website — and at least one of its menu items is pointing to a node. You think of an improvement to that node's content, so you edit the node and save the results. But its corresponding menu item has disappeared from your custom menu, and has somehow reappeared on the Main menu! How did that happen?