I've just noticed, as I was creating the SR2 version of the famous SimplePlanes flying toaster, that detachers cannot be attached to wings except at the end points, nor can interstages. I suppose I'll have to find a work-around for this in the mean time.
Suggestion
Implemented
Fixed in 1.3.111.0
Perhaps give wing a surface node so anything could attach to it, especially pylon, decal, lights, rotators for extra control surfaces / landing gear