Applied patch https://drupal.org/files/issues/Issue-1357402-Header-declared-as-string-instead-array.patch to backup_migrate module. Actually patch didn't really apply; added the if(->mimetype() == 'application/x-gzip') statement to line 325.
Merge pull request #17 from jordanlgraham/backup_migrate_patch

Applied patch https://drupal.org/files/issues/Issue-1357402-Header-decla...