I was experimenting with mechanical crafters on minecarts and discovered the following. If you activate the minecart assembler while the crafter is crafting, it will spit out all the ingredients, and pause the craft, once the crafters are placed back in world however; the craft will resume and give you the result, meaning you now have both the ingredients and the result.

Addendum, if you keep alternating constructing and deconstructing the cart contraption it keeps spiting out items, doesn't even need to be a valid craft if you force the crafters with a redstone signal

Issue should now be fixed in dev branch, thank you for the report!