There was an optimization which avoids the need to replicate/copy all design documents from the "master" database (a couch database named "master"), which stores only design documents, to all the local vbucket couch databases. This optimization avoids a huge number of couch local -> local replication that consume too many resources and introduce a small delay in propagating the design documents.
However, the compaction daemon (in ns_server, but very, very, very similar to the one in couchdb repository) is looking for design documents in the vbucket databases in order to find which views each has. This is a noop, and it has to get the design document names from the master database instead.
The corresponding couchdb change is:
The ns_server and couchdb compaction daemons: