After deactivation of Path module, the URL aliases are not deactivated. The table url_alias is not emptied. URL aliases are still active. Basically, deactivating Path deactivates the Path GUI and adding of new aliases, but *not* the functionality for existing aliases. This may be a desired and useful behaviour, but it is not obvious to the user.

It should be made clear to the user that she needs to delete all URL aliases before deactivating the module in order to remove the functionality for existing aliases. A hint after deactivation on the modules page would do. Something along the lines:

"Path module successfully deactivated. Existing aliases remain active in order to prevent possible incoming links from breaking. To remove existing aliases permanently, delete them before deactivating Path module."

Drupal version 6.13