RUBY-554 showed us that we have a number of issues within the JRuby extension currently wrapping the Java driver's BSON package. Much of what is there is messy and unnecessary in later versions of JRuby.
This ticket is to track the effort to properly evaluate the need for the current code and future of this part of the Ruby driver.
Some resources for research:
http://jruby.org/apidocs/org/jruby/javasupport/util/ObjectProxyCache.html
http://jira.codehaus.org/browse/JRUBY-6506
https://github.com/jruby/jruby/wiki/Persistence
https://github.com/headius/weakling