After upgrading my M0 Isida to 50/50, the M1 did not become available as a finishing upgrade as it had when I fully upgraded the M0 Hornet...apparently this is because my rank unlocked the M2 option, and erased the M1 final upgrade just as I made it there. Now there is no place to 'graduate' to M1 and I am stuck with an M0 50/50. So now what? If there's no way to reverse this or be allowed to earn the M1 after all my work...well you know the rest.