Kerbal Space Program

Tested with the provided craft. When launched to KSC pad or runway, because gravity, weight of suspended parts acts as a force to displace joints, until joints reaction force (an elastic force proportional to displacement, totally managed by Unity physics) equals weight. Exited to KSC, back to the craft (which causes the craft to go on-rails/off-rails): of course gravity is still there and acts again to displace joints.
However you said the displacement is maintained even if the force is gone: easy way to test, sent the craft to orbit (close to SOI limit to have as little gravity possible, but anyway gravity acts on all parts the same way, so there's no force acting on the joints). As expected, all parts had reverted to their normal position, no joints displacement.

But of course I may simply have not understood how you intended to perform the test. In internal testing, a sequence of steps required to reproduce the issue is added to the description, something alike:

Reproduction steps:
1. Start KSP, open a new sandbox game
2. Load the provided craft file in editor (VAB? SPH?)
3. Launch craft
4. Observe joints displacements
5. Cheat craft to orbit, 80000 Km above Kerbin
6. Observe joints displacement
Result: joints are no more displaced

Please show us how the issue should be tested to produce the result you consider an issue.

Hi, thanks for your reply.

I got some screen shot, they may explain better than i do.

For more description: When the craft is reloaded the second or more times, the previous displacement will not generate forces to against the weight, so the parts have to displace more. It's like every time we exit and reload, the game turns the previous elastic deformation into plastic deformation.

My test steps:
1, launch the craft and decouple the weights: all displacement recovers.
2, launch the craft, exit, reload, decouple the weights: all parts below dlc part will not recover.
3, launch the craft, exit and reload multiple times, then decouple the weights: those displacement are accumulated.

Changing to updated since the previous user forgot to do so.

Yay, good catch! Couldn't get at first what you intended, but eventually got it works with "quit to Main Menu, then reload the saved game, return to that craft". Took about 9 repetitions to displace those joints enough to safely land that tank, and then those joints stay displaced exactly as you said.

1.8.1 and it still happens. The engines on my plane is getting this bug constantly. Several physics reloads and it's screwed up completely.