Pretty sure that the floating origin moves with the craft now every frame. The entire universe also orbits around the craft when it is below the inverse rotation altitude threshold, which means that PhysX is doing physics in the co-rotating reference frame. That means that the "First point of Ares" -- normally (1,0,0) -- rotates around the z-axis as the craft moves and you have to query Planitarium.right to determine what its current orientation is. That means that tick-to-tick coordinates change, which makes trajectory optimization hard because values in the future won't match at all. You have to remove that rotation to get something like actual inertial coordinates (after also removing the offset origin to the vessel as well).
They've also recently fixed issues with single precision calculation in KSP1 and used a double-precision QuaternionD.LookRotation in the maneuver nodes to keep interplanetary trajectories from hopping around a lot.
[ oh it also uses left handed coordinates, which is terrible which means (0,1,0) is the north pole and the left handed cross product gets used so dual vectors like angular momentum point south for east-going orbits -- except the Orbit class uses normal right handed vectors and when you forget to .xzy swizzle a vector for one reason or another you can wind up debugging an issue all day long ]
