The bug in that slave version of a table with unique field still was
able to execute INSERT query as replace whereas it's impossible on master.

The reason of this artifact is wrong usage of ndb->extra:s.

Fixed with resetting flags at do_after.
There is open issue with symmetrical resetting
   table->file->extra(HA_EXTRA_NO_IGNORE_NO_KEY)
which i had to hand to bug#27077.
The test for the current bug was committed in a cset for bug#27320.