The T1 runway is the only runway. The "upgraded" runways are only a graphic effect. They have NO COLLISION. What we are driving on is the same old crappy gravel with the pot holes and little hills, not the smooth flat paved surface we are presented with.
Your landing gear is dipping into and over these very large imperfections in the T1 gravel runway, hidden under the paved runway model. That's why it suddenly goes one way or another, and why it seems to go randomly left or right.
Temporary workaround until this is fixed: Use the flat ground left of the runway. It's ACTUALLY flat, and will not make your plane suddenly steer left or right on it's own.
Don't believe me? Build a little lander probe with landing gear and launch it on the runway. Watch it sink into the runway model and settle on uneven terrain below. Good luck!