We don't have any default databases for MX systems saved anymore but we have AX. For some reason I thought it was ok to load a default AX database to the MX and it works because actaully both sytsems or on the file that we are putting on the flash card or am I wrong?

from the Mitel docs:

Database Conversion
There is no database conversion facility available to facilitate the migration of database from
any other variant of SX200 ICP controller to 200 AX and vice-a-versa.
You can restore an AX Database on the AX controller, but the system would restrict you if a
database from any of the other platforms (CX/MX) is restored.