google-cloud-ruby: `assertion failed` error on multi core machines with google-cloud-logging ruby gem

Our environment:

Ruby: 2.1.5
Rake: 10.4.2
Rails: 3.2.13
google-cloud gem: 0.32.0
google-cloud-logging gem: 1.1.0
grpc gem: 1.3.4
google-protobuf gem: 3.2.0.2
Docker image: ruby:2.1.5

We are pushing logs to Google Stackdriver from our Rails app using google-cloud-logging gem. We are using Docker to package and run our app. When we run any rake tasks of our app (inside Docker container) on multi-core Linux machines we are getting this error.

E0613 15:27:13.484736145      12 sync_posix.c:47]            assertion failed: pthread_mutex_destroy(mu) == 0
rake aborted!

The same Docker deployment is not causing any issues on single core Linux machines or multicore OSX machines. When we remove the stackdriver related code from our app, this error is not reproduced. Where am I going wrong?