MariaDB seems to behave differently from other databases when selecting a time with a datetime. Maria requires truncating the date first, otherwise it returns the empty set. MySQL, Postgres, Sqlite, and SQL Server ignore the date and return rows matching the time portion.
Here are the examples:
https://gist.github.com/bronson/0a49e7d3fe7242cb5cd3 (thanks to litheum for this table)
Monty says: what looks wrong at my end is that we are converting the string to this time: "838:49:59.99999" and then trying to compare that. This is stored in a Item_time_literal.