Memory engine table giving inconsistent results

Using MariaDB 10.6.7-MariaDB-2ubuntu1.1-log - Ubuntu 22.04

I have a relatively complex application that is making use of temporary memory (engine) tables. The tables are generated from select insert statements and then the data is manipulated. After which a series of selects are performed with one or more rejoins to the same table.

The tables have 8 indexes created with the table create statement some are hash and some are btree.

Doing exactly the same process using exactly the same data I am getting slightly different results (in terms of data return and the number of rows).

It's taken me a while to get to the root of this, I have figured out that the temp memory tables are identical in terms of data and the database calls are the same.

I have let the tables be created as permanent memory tables so I can see them in myphpadmin, rename them, and let them be created again. Then run the same query against each table, and I get different results. The table checksums are identical, row count is identical. but the same query gives different results when tables as memory engine. Convert them both to INNODB and both give the same result... is the memory engine broken?