How do I prevent LastPass from filling erroneous form fields?

As an example, let's say you are on https://www.google.com/ and there is a field on that page that LastPass is filling with the value 'abc123'.

To prevent LastPass from filling in the value, follow the following steps:

1. Locate the site in your LastPass vault that contains the data 'abc123'.  The easiest way to do this is to go to your LastPass vault and search for 'google.com' to list all matching sites.
2. For each matching site, click the Edit/Pencil icon to bring up the site's Edit dialog, and then click on the 'Advanced Options' link, then 'Edit Form Fields' link to bring up the Edit Fields dialog.
3. Look for the field with a value of 'abc123' and click [-] to delete the field.
4. Click 'Save' to dismiss the Edit Fields dialog