The description on the Listing Details page is considered general since all users in your subscription will have access to it. Any adjustment made will be reflected in the account for all users. The description on the Post Ad page is personal. The user who composes it will be the only one who has access to it. This description will then be used in the ad for the property on the user's YGL issued website (Public URL).
When you click the Post Ad button for the first time, the description you have on the Listing Details page will automatically transfer to the description fields on the Post Ad page. All subsequent changes made to the description on the Listing Details page will not transfer. This means you are required to manually adjust the details on the Post Ad page if you wish for them both to reflect the same information.
If you would like the Public URL to reflect the description that is on the Listing Details page, you will need to navigate to the Ads tab, search for and select the entry for the desired property and use the Delete button at the top of the page. The Ads tab shows the entries you have documented a personal description for. Deleting the entry on this page will not remove the listing from your database, only your personalized description.