I've downloaded last version of your dbExpress driver.
Now when I connect to MySql with database name "DB1" and execute
DS.CommandText := 'use DB2';
DS.ExecSQL();
then I try t execute another query
DS.CommandText := 'SHOW INDEX FROM tableOnDb2';
DS.Open; <- It raise an exception "root.tableOnDb2" doesn't exists".
With previus version of your dbExpress driver it work fine !