Normally you can swap items between the crafting window and the inventory, including items that are equipped. For example, you've opened a Recycle Item blueprint and dragged a sledgehammer from your inventory into it (i.e. you can see the metal scraps that would result from recycling the hammer, but you haven't proceeded with recycling it yet). Now if you have a knife that's equipped, you can drag that knife to replace the sledgehammer in the crafting window, and the sledgehammer will then replace the knife in your equipped slot.
That's the expected behaviour so far. The unexpected occurs if you happen to be wearing a suit of riot armor with a shield. This prevents you from equipping two-handed weapons, so the sledgehammer from the example couldn't get equipped. It doesn't go back to your inventory either, it just disappears into thin air. As far as I can see, this can only happen with the two blueprints of Recycle Item and Disassemble.
