RubyGems dependency API 500 error for virtual repositories

We have a setup a gems virtual repository containing a remote repo and a local repo.

When trying to do bundle update with this repo as the only source in Gemfile, artifiactory returns with this error:

Fetching gem metadata from http://artifactory/artifactory/api/gems/rubygems/.
Retrying dependency api due to error (2/4): Bundler::HTTPError Net::HTTPInternalServerError: {
  "errors" : [ {
    "status" : 500,
    "message" : "Comparison method violates its general contract!"
  } ]
}

When listing the remote and local repo in the Gemfile separately all works without error.

Seems someone else also encountered the same problem:
http://forums.jfrog.org/Ruby-Gems-Dependency-Issues-td7580610.html