I to have noticed instability after the 1.4.x updates. I have a lander (leg: LT-05 Micro Landing Strut) and buggy (wheels: RoveMax Model M1) that I have used to almost every planet in the system but now when I try to land on Duna, as a test run, the legs on the lander vanish and the buggy never settles and just bounces around till it explodes. I haven't tried any other planets yet.
I think these updates have messed up a lot!
I have seen this bug on rare occasions at the landing pad in the past but the game would reset and calm down the physics if the ship self destructed.
Hopefully this can be ironed out soon, I dare not play my career mode till it is.
Is this being worked on?