These changes that seem to be just happening are occurring based (1) the presence of the optional AddressAccelerator module being present and (2) a setting in Business Rules set to automatically validate addresses when an existing address is edited. To get the desired change to save:
  1. Go to Config > Business Rules
  2. Click on General
  3. Find When editing addresses...
  4. Unmark Automatically attempt to validate the address
  5. Click on anything in the left Raiser's Edge menu to save this change (Query, Records, etc.)
  6. Return to the desired constituent record and complete the address update
  7. If you wish to restore this setting, return to Config > Business Rules > General and re-mark Automatically attempt to validate the address
Note: If you wish to leave this unmarked, an address can still be validated directly from constituent records using AddressAccelerator.