This seems like a bug, especially as the system cuts down to a single unicorn temporarily very shortly afterwards.
The number 2 is hardcoded, as is the number 1 for the reduction.
Edit: looks like this change introduced the inconsistency
https://github.com/discourse/docker_manager/commit/8bfea831c7b423d26d85585f9a3d7301d58e00ae
I think your post (and this reply) should be a in a new thread, in the bugs category.