How is that possible? When you have a long train with engines at both the front and the back, are you saying that the coupling between the rear locomotive and the car just ahead of it is not in compression?Railroad cars have mating buffers that absorb the push.
The coupling links are slack in such circumstance. They are never in compression.
I've only seen mating buffers (or what I think you mean by that term) on cars that have tensioned chain linkages. I don't recall ever seeing any such buffer on a typical railroad car that uses the normal coupling (or at least what I think of as the standard railroad coupling). For instance, consider the following image (snagged from Google):
Where is the mating buffer and how is this coupling not under compression if one car is pushing the other?