I actually found some tilting in ufo mode, with the help of the HUD horizon line. Keeping the head level in the center, it would slightly tilt just by looking up or down with the mouse, and the tilts are opposite in up/down views. As far as I can see, this tilt is produced by the auto-roll control, which keeps the roll aligned with the gravity vector when you are close to the planet's surface. It does some unexpected things when the pitch is high. This thing has been there for a long time though. I'll try to fix it, but this tilt is certainly not that severe as on your screenshot.