Hello,
I look, and if you craft an iron crate with an none-empty Wooden crate right now it will void all the content. I think the recipes should keep the inventory, because the recipe is made question to upgrade the lower tier to the next tier of crate. Right now I have to completly empty it question of upgrade the Wooden Crate to the Iron Crate if I don't want to look the content...

You should possibly make sure to keep the upgrade already installed when upgrading to the Iron Crate.

Version:
BDS&M: 0.0.24
Minecraft: 1.12.2

Fireztonez