[1.10.x] Near Future Technologies (All 1.10, NFA returns)

I found a bug with the Adapter 75-L2 Lower Stage Engine Mount. It's not possible to mount an engine (any size) in the middle slot in any configuration (holding Alt or not.) The mounting slot for the engine is there but the 7.5m central slot blocks the smaller one. There's a workaround to mount it in the central 7.5m slot as seen here and move it with the move tool. I'm not sure if this can be fixed at all, it might be KSP's fault altogether.