Just a heads up, The Steel Door can be used for seeing through the world. Obviously not a huge problem of Single player, Just thought it might cause issues on the DMU.
(For the record, this screenshot was taken on a Single player world, not the DMU. Notice how I've got items from another mod in my hotbar. Just clarifying so you don't think I took it on the DMU, which would be reason to ban me)
This is known, and patched for the next release.
Thank you for reporting and clarifying though.