My inventory was mostly empty while crafting and I noticed there was a standard copper wire laying on the ground where I had been standing (maybe dropped from an error in the splitter crafting?). There were also several instances of "Not enough ingredients" in the console that I hadn't noticed while building.
I hit Q while holding the 4.3G stack and it filled my inventory up with 64 stacks of conveyer.
I had assigned that slot to the yellow conveyer belts (with middle-mouse click) just moments before if it's any help.
I'm almost certain it had something to do with me placing the belts and crafting recipes that require them at the same time. I think it decided to use the stack of belts I was holding/had picked up to craft with. Somehow it drive the item count below zero and a "wrapping" error occurred with the item count variable?
The save game from just after the glitch occurred (but before my inventory filled up) is attached in case it's any help.
Yeah, I thought about carpeting the map in them to see what the biters would think of it. I managed to get the stack into a chest before it re-stacked and blasted it to death with my pistol to salvage my savegame though. Die demon! 
