"Null" string interpreted as null value on save

inserting a string value of "Null" in a text field results in the value being interpreted as mysql null – and no value being stored in the db. for example, create a new contact with the name "John Null" – after saving, it appears the value was saved correctly because the constructed display_name includes the full name, but if you view the record in the db or return to the edit screen, the last name value is empty.

this is reproducible in the 4.3 sandbox and is present in prior versions as well.

we've been unable to find a simple solution that does not involve altering the PEAR lib.