Yes, that headline is confusing.
I have a SLDPRT (simple part) file that contains several layout sketches for a gearbox I'm designing, which I use in the layout of various other Derived Parts. This way, I can change gear sizes by editing the sketches in the main layout part and all the other Derived parts change accordingly. This all worked so well in SW 2010.
When I moved to 2015sp5, one of my derived parts broke. The various sketches in my layout part have been shifted and moved around when viewing them from the derived part. When opening and viewing actual layout part itself, everything is fine, but in the context of the derived part, things are torn asunder - the individual items (sketches) in the originating layout part are not held in relation to each other, despite the layout part being properly located withing the context of the Derived part (ie. origins aligned).
Does anyone have any input on this?