Dont have a clue
The terms stability, stable, and unstable have specific meanings with respect to the flying qualities of an airplane. Those meanings are confined to "static stability" and "maneuvering stability" and refer to control force gradients vs. speed, and vs. normal acceleration ('g') respectively. Unfortunately, in common practice the terms are used indiscriminately by "aviation experts".
The software changes (implementation of the -908 FCS load, and some subsequent set mandated by the FAA to allow certification of the MD-10 on the same type cert) improved the predictability of the MD-11 in the landing phase; they did nothing to correct the omission of a simple lead-lag pitch SCAS (à la F-4) which was designed into the Rate Command CWS of the LSAS (which is there, but set to zero gain, making it non-functional), which would have compensated for the extremely low short period natural frequency of the airplane in the landing configuration (making the airplane prone to APC). The change in geometry from DC-10 to MD-11 made this item a required addition from a handling qualities standpoint, yet the FAA still certified the airplane. They also did nothing to correct the gross elevator load feel (force vs. displacement) gradients in the landing configuration, which make it virtually impossible for a normal pilot (and in particular a soft-handed airline pilot) to access the necessary deflections for control of the airplane. Nor did they compensate for the inadequate bandwidth of the elevator hydraulic actuators, which incur significant lags when rapid elevator control inputs are required (as in turbulence).
The DC-10, and MD-10, does not suffer from the above problems for several reasons: it has a lower max landing weight, and thus much reduced pitch inertia (Iyy), the elevator throws required for adequate control are significantly reduced as a result of greater elevator control power (area) along with correspondingly lower required control forces. Additionally, the DC-10 (as employed at most airlines) does not employ RCWS, a ludicrous, parallel roll control "enhancement" on most MD-11s; FedEx, incidentally, ordered its airplanes to have RCWS turned off; a wise decision.