Hm, well that's pretty annoying. The item "macguffin" is flagged as "not stackable", but the recipe takes an input of 5 macguffins. When attempting to reverse the recipe, it attempts to set the output as 5, which can't be done since the stack limit is 1. I could either make all recipes with "not stackable" ingredients on the no-recycle list, or set the recycle output to 1. I'm not sure how important this item is... but the simplest option is to just make that specific item non-recyclable.
Which is what I ended up doing; should be fixed as of v8.1.19
