Decoupler bug when attached in reverse

[Turbo Ben]

I came accross a bug recently when doing a Mun mission.

This bug affects in line decouplers (the TD series) when attached in reverse, ie, when placed so as to remain attached to the main vessel rather than discarded. I've done some testing with all sizes of decoupler and they all behave unexpectedly.

Simple craft to test: command pod, fuel tank, radial engines attached to tank, decoupler placed upside down to normal (by pressing "d" twice before placement, arrow on decoupler pointing down), another command pod.

Expected behavior: when decoupled, the lower command pod should be detached with the decoupler remaining attached to the upper stage.

Observed behavior:

TD06/12/37/50: When staged, decoupler detaches from both sides and falls away (similar to TS variants). However, game acts as though decoupler is still attached. Camera drifts off center as distance from decoupler increases. Decoupler is still visible in the parts manager.

TD25: Explodes when decoupled unless ejection force is reduced, in which case it behaves as above.

I haven't been able to recreate this, but when I first discovered the bug in orbit around the Mun, I tried quickly switching between active vessels with "]". Doing this caused the lander to spin with such force that all parts were flung from the craft leaving just the command pod.

[Radprosium]

Yeah can confirm, there are a wide range of bugs regarding simple decouplers (not separators) when using various configurations : 

- decouplers not detaching on the correct side but on both, 

- decouplers not decoupling at all when attached to an engine with a fairing

- decouplers detaching but then being considered still attached to the ship despite being 10m away, with the behavior passing from one ship to another ship when reloading save 

- jettisoning a fairing between an engine and a decoupler acts like decoupling, (no more control over parts) but the ships is still connected

- witnessed a decoupling but controls still remained on both the ships

All this was tested on a basic Appolo - style launch, and clearly the decoupling, turning, redocking, decoupling LEM etc creates various problems, and saving / reloading sometimes changes the behavior and sometimes for the worst.