I was checking the last snapshot and I found than in igloos where there's a basement, there's one potion of weakness that, like popped out, from the Brewing Station, and it's sitting right there just like an item. The same happens with a cactus that popped out of the flower pot right there. Though, there's still a cactus inside the pot.

I don't know how many potions do Igloos have but with there's one as item and one that's inside the Station. Here are the steps to reproduce:

• Create a new world in the snapshot 18w43a.
• Locate an Igloo using the chat commands
• Teleport to an Igloo and check if it has a basement. If true, go to the next step. If not, try again with other seed.
• Go downstairs to the basement an look to the brewing station and the flower pot. You will see a potion of Weekness and a cactus laying aside of those.