Profile/standalone form errors in 1.7 & 1.8: data moves from 1 contact to another

1) The short version, based on testing at the sandbox using 1.8 alpha:

• I created a new group called Volunteers.
• I created a new profile called Volunteer, featuring fields for First Name, Last Name, Email & Phone.
• I clicked the link to generate the code for a standalone form from the Volunteer profile.
• I pasted that code with no modifications or additions into a new test Volunteer page on our site.
• Using the new test Volunteer form, I entered information for "Test Testguy" with email address test@tester.com and phone number 555-555-5555.
• I searched for this new contact in the sandbox CiviCRM and found him at:

http://sandbox.civicrm.org/drupal/civicrm/contact/view?reset=1&cid=108

• But the new contact has physical address information from somebody else, when he should have no such info since there are no fields for it in the form:

1115 W 7th St
Erie, PA 16502-1105
United States

• I can't find any other contact with this address among the sandbox contacts. I think that's because the information is actually being moved from an old contact to the new one. This is what happens with our install (v 1.7.9821).
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2) More detail, based on my earlier problem in upgrading from 1.6 to 1.7 (see http://forum.civicrm.org/index.php/topic,642.0.html):

After upgrading from 1.6 to 1.7 I find:

• My profiles, which were working fine, are gone. So our standalone Volunteer form now points to a non-existent profile and fails.
• I created a new profile and Volunteer form, but in testing the form it appears to fail with "DB Error: already exists" and (for example) "nativecode=1062 ** Duplicate entry '3220' for key 2" (full message below).
• Yet the test Volunteer form submissions do end up in the database - except that their data is mixed with existing information from other contacts (alarming behavior!). So a new test user will have the same, say, physical and email addresses as an existing user. I imagine this is what's causing a "duplicate entry" error.

We're running MySQL 4.1.9, PHP 5.2.1 and Apache 2.

Full error message:

Sorry. A non-recoverable error has occurred.
Database Error Code: Duplicate entry '3220' for key 2, 1062

Return to CiviCRM menu.

Error Details:

Array
(
[callback] => Array
(

• => CRM_Core_Error
  [1] => handle
  )

=> -5
[message] => DB Error: already exists
[mode] => 16
[debug_info] => INSERT INTO civicrm_address (location_id , street_address , supplemental_address_1 , city ) VALUES ( 3220 , '5959 Downtown Place' , 'Suite 2' , 'Testerville' ) [nativecode=1062 ** Duplicate entry '3220' for key 2]
[type] => DB_Error
[user_info] => INSERT INTO civicrm_address (location_id , street_address , supplemental_address_1 , city ) VALUES ( 3220 , '5959 Downtown Place' , 'Suite 2' , 'Testerville' ) [nativecode=1062 ** Duplicate entry '3220' for key 2]
[to_string] => [db_error: message="DB Error: already exists" code=-5 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_address (location_id , street_address , supplemental_address_1 , city ) VALUES ( 3220 , '5959 Downtown Place' , 'Suite 2' , 'Testerville' ) [nativecode=1062 ** Duplicate entry '3220' for key 2]"]