Noticed this on the Crucial server.

If you try to deploy a ladder downwards and can't because the bottom of the ladder is blocked by something, vanilla ladder placement logic will take over. In my opinion, this is undesirable - if you're deploying a ladder on the side of a vertical 1x2 shaft for example, you'll end up placing a ladder on the far wall, and have to clean it up.

I think it would be better if attempting to place a ladder against a ladder in this state just did nothing, instead of deferring to the bad vanilla behavior.