Plugin pack missing installed plugins

I am trying to use plugin pack to export plugins to systems without connectivity. I am attempting to test out the functionality with a simple plugin provided by Elastic - logstash-input-example.

After building and installing the logstash-input-example plugin, I can verify that it is installed by running a plugin list command.

When I attempt to pack all installed plugins with the command plugin pack, the generated plugins_package.tar.gz does not contain the plugin logstash-input-example. Any ideas why pack is missing some plugins?

I am using Logstash 2.2.2 with Java 1.7_79 and OSX 10.10.3