Thanks for answers! Yeah, but logically if it is merged, highlighting icon of merged module should highlight all individual modules in pack, not single random module. I use it to check if staging is in proper order and with only one part highlighted, it is very hard to check decouplers. Highlight itself could be more visible too... ah well. It happens without any warning and I find it confusing. Unfortunately, I am not sure how to fix it UI-wise. Well... now when I think about it, pulling apart and reattach would be sufficient, provided it works properly. I got impression that when reattaching, program tries to recalculate possible staging configuration from scrath (ant it can have different result from staging created when user manually add components, not to mention cases when user changes staging itself too)... deattached parts should remember their staging config. Sure, multiple detach, reattach at varying points would eventually messed up it beyond recognition (forgetting all manual changes), but at least it would work for simple cases as 'adding forgotten SAS in middle of rocket' without hassle.