GitLab 8.3.x ships with gitlab-workhorse 0.5.0, not 0.5.1

I noticed this while trying to debug an issue with gitlab-workhorse. With GitLab 8.3.1:

$ sudo cat /opt/gitlab/embedded/service/gitlab-rails/GITLAB_WORKHORSE_VERSION 
0.5.1

But the actual version reported by gitlab-workhorse:

$ /opt/gitlab/embedded/bin/gitlab-workhorse --version 
gitlab-workhorse 0.5.0-20151228.061801

Is this a mistake in the build or tag procedure?