Actually, I have the same problem. It is not related to some altitude, but it always happens, when I right-click to change my viewpoint in the cockpit. When I do this, the yoke of the aircraft pitches down and banks, although the autopilot is on, but the aircraft doesn't change its flight path. On my second flight, the EGT even rose, which gave me a master warning combined with the cabin altitude changing. After downloading V1.0.1, I hoped that the problem was fixed, but it still happened. Attached are photos of my most recent flight, where the altitude first went down to around -30000ft and later went up to about 320000ft as shown in the picture. It has to be a bug because the aircraft obviously isn't flying at 320000ft, and all the switches are in the right position. I hope that this information is useful because this bug is extremely annoying.