All new doors stack and turn into old oak ones in your inventory when picked up.

Put the summary of the bug you're having here

Miss-placed new spruce door (but works with all doors) and picked it up while having an old door in my inventory.

After collecting the old door from the ground I could not find it in my inventory, then realized I had more oak doors then I began with

Pick up any of the new doors with an old one in your inventory, will stack as and oak door.