When making a custom smelter, I get a broken block out of it.

I'm making a mod that has a custom smelter, the way it works is I click a button and it puts a birch bark into an output slot. But when I click the slot to get the birch, it flashes and goes away, right out on my mouse. If I shift-click it, it's fine and goes into my inventory, but if I click it again, it goes away. If I don't click it and keep it in my how bar, then place the birch log block, it flashes quickly and goes away.

That's my only code besides the "rightClickBlock" to open the GUI and that works fine.

Here's a video: https://imgur.com/a/vC8irRH