I have some space plane designs that seem to work on the first use or so, then start rolling right after a few days (weeks?) of play. The problem seemed to get worse after moving a craft from one installation of KSP to another; both were 1.3.0.
On a lark I tried deleting physics.cfg and partdatabase.cfg, and letting the game rebuild those. That seemed to work for some folks dealing with broken parachutes, and it 'fixed' my roll right problem. But I wondered if I was cheating somehow by doing that.
I usually use Ferram Aerospace Research for the extra challenge. I've already asked over at the FAR thread, but no one's responded. I don't use other add-ons that mess with the physics or the stock parts. But FAR or Stock, am I cheating myself by having the game rebuild those? On the craft in question I've double checked and triple checked symmetry to make sure everything was even.
--