Change 4848 (Zone types "primary" and "secondary" can now be used as synonyms for "master" and "slave" in named.conf.) appears to have caused the xfer system test to start failing:

  :
I:testing ixfr-from-differences yes;
I:testing ixfr-from-differences master; (master zone)
I:failed
I:testing ixfr-from-differences master; (slave zone)
I:testing ixfr-from-differences slave; (master zone)
I:testing ixfr-from-differences slave; (slave zone)
I:failed
   :