Problem: the table's INDEX and DATA DIR was taken
  directly from the table's first partition.
  This allowed rename attack similar to
  bug#32111 when ALTER TABLE REMOVE PARTITIONING

Solution: Silently ignore the INDEX/DATA DIR
  for the table. (Like some other storage engines
  do). 
  Partitioned tables do not support DATA/INDEX
  DIR on the table level, only on its partitions.