Material Graph Glitch - Lost texture map node after save and close

[cgreg]

Hello -

I am wondering if I found a glitch, or if this is how the material graph is intended to work. I have multiple pieces of artwork that I want to apply to the side of an object. When I have multiple texture maps, if one or more is disconnected (not being used) I notice that they all get deleted when I save, close, and reopen the .BIP file. Why does this happen? I still need them, depending on which concept I'm rendering.

(attached screenshot)

Thanks -
Chris