The merge of MySQL 5.7.9 into MariaDB 10.2.2 introduced an incorrect conflict resolution in row_fts_merge_insert().
The assignment space=table->space was removed, and to ‘silence a compiler warning’ an incorrect assignment space=0 was added.
I noticed this when working on a merge
MDEV-12634 from 10.1 to 10.2.9. That merge will fix this issue.