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.