Quote - ... This is Poser 7, so maybe - hopefully - this behaviour is fixed in later versions. Any light you can shed (no pun intended) would be welcome... 

When creating a key on a material input, Poser creates not only the parameter ("SegA_PoserSurface_6" in your case), but also a dial and a channel on the prop. It looks like:

                shaderNodeParm SegA_PoserSurface_6
                        {
                        name SegA_PoserSurface_6
                        initValue 0
                        hidden 0
                        forceLimits 1
                        min 0
                        max 10
                        trackingScale 0.01
This shaderNodeParm however is attached to the actor, not the material, and it does not get saved into the mt5 or mc6 file. So when simply loading the mc6 or mt5 it will not work. I tried to copy the section with the shaderNodeParm into the mt5, but then i get a crash, too (using Poser2010). Perhaps it is a similar case like the missing ability to create new morph channels when loading a pose file. When saving the whole prop, the shaderNodeParm is saved with it and everything seems to work (the actual animation data, however is not saved with it when using a prop, so you either need to make it into a figure and save a pose file, or put the animation keys into the channel with a text editor).