So at this point I would like to sort of merge this issue with my previous post thread ([url]https://forum.vassalengine.org/t/deck-behavior-unexpected-and-non-responsive/8797/1]). I rebuilt the module from scratch, using the Prototype that was abandoned (per previous thread) and all of the other commands exactly as before but leaving GKCs alone. The rebuilt module works exactly as it did before my attempt to achieve deck-to-discard functionality broke it; evidently the Prototype, which seemed to be at fault before, was not the root cause of the original deck failure.
Interestingly, the new module is less than half the size of the old module was (despite appearing to have the same number of image files), even before I attempted to add GKCs to the old module. It would seem that there was indeed some sort of file or directory corruption; I have retained the old module if it becomes of interest to anyone.
I intend to make a test copy of the new module for GKC tinkering; I will report anything that seems helpful.