Luckily, turns out it's random. Happens only with module installed, but only about once in ten, so going to the space center and back to flight usually fixes it. And second thing, it seems it's not that they aren't closed. It is just an enormous lag with closing. I have weak computer, so yea... Sorry I bothered you. Feature request: Could you make a decoupling force defined in decoupler's file a medium one? I mean, I would like to see the bar to be 50% full on them, so we could not only weak them, but also make them stronger if needed. I understand that allowing for example more fuel would not make sense, but stuffing more explosives, or stronger ones, is not that hard, and they are negligible % of decoupler's mass anyway.