A new patch that fixes the underlying history problem...

It checks the DB to see if the prop value exists before trying to fetch
it from the DB. This stops the value in the form from being fetched if
there is no value for the prop in the DB.

This probably isn't the most elegant solution, because it requires
hitting the DB twice if a prop value does exist in the DB (instead of
just once), but it is preferable to rewriting or duplicating a decent
amount of code.