I didn't think it allowed you to select mssql if you have a mysql database

The reason you don't get any results for internal indexing will probably be that you need to reindex the database after you've changed the index to internal.

You may find that it is a problem with the database that is causing the change to mysql not to work - I've had this in the past. If you turn on debugging and run the index change from shell you should be able to see what is happening and if there are any problems.

Other than this, I'm not sure what to suggest. If it appears to be working maybe you should just leave it.