Steps to reproduce:

Go to "Post Settings" and set Preview Post to Required
Create content, give it a friendly url (eg: "test")
Edit content, change friendly url (eg to: "test2")
Click Preview, then click Save

The URL is not changed and the database is corrupted. To see the corruption, continue with these steps:

Go to "Post Settings" and set Preview Post to Optional
Edit the content and change the friendly url to the same as attempted before (eg: "test2")
You will get an error:
"user warning: Duplicate entry 'test2-' for key 2 query: UPDATE url_alias SET src = 'node/1', dst = 'test2', language = '' WHERE pid = 1 in C:\wamp\www\drupal\modules\path\path.module on line 100."