sbt/sbt-ghpages-plugin — pull request #3 by etorreborre (2012-05-24 07:17:16+00:00)
Title: Don't delete files in the staged repository when synchronizing

The documentation says that the push task must not remove the existing files in the staged repository (because the clean site task allows to do that), then I think that this line should be removed from the synchLocal task.