If a table description already exists on the database but has been edited via the model in Toad, the alter script generation via the Sync & Convert Wizard appears to mishandle this situation. Instead of using sp_updateextendedproperty, it uses sp_addextendedproperty. Attempting to run sp_addextendedproperty for a table that already has a table description results in the following error:
SQL Server Database Error: Property cannot be added. Property ‘MS_Description’ already exists for ‘dbo.table_name’.