On-disk Temporary Tables Are Leaking

It would appear that temporary tables that get created on disk are being leaked. A lot of #sql*.ibd files get left behind in /tmp and never get reaped, even though most of them do not have open file handles (checked with lsof).

There are no user-processes running on the server, only replication (from multiple sources) so it is somewhat mysterious that the temp tables are getting create in the first place.

This may be related to MDEV-4015. I'm wondering if it is possible that the reaping function is looking for MyISAM tables (aria is the default engine for temp tables, a compile time option), but since the default storage engine is InnoDB, the tables get created as such, and the clean-up doesn't catch them.