The tendency might also be a function of the wing downwash. At some speed it changes it's angle enough at the LE of the stab to do the deed. A tail with a longer moment could be in a less radically changable environment. And/or the tail might be so close it's getting greatly disturbed air from the wing in one situation (and it's enough to change radically the tails ability to control the a/c's pitch) and only slightly disturbed air in the other. Or both situations.

Also, the drag on poorly streamlined gear, like just round wire and wheels would be, usually equals the drag numbers you'd get from the airplane without gear. So gear drag is definitely significant.