Saving form value for address standardization provider fails

on civicrm/admin/setting/preferences/address, on 4.2.6 Wordpress, I am not able to get the dropdown setting for "Address Provider" to stick. User ID and Web Service URL save correctly, and the form also validates correctly (e.g. "You must provide values for all three Address Standardization fields."), but the Address provider does not save and therefore Address Standardization never works.

The workaround for me was to set this value in the backend, through the civicrm_settings table (s:4:"USPS".

For those getting this to work with USPS, note that the testing servers will only work with two addresses, one of them being 6406 Ivy Ln, Greenbelt, MD (will note this in the Wiki).