Can't "gem install bundler" under rvm

gistfile1.txt

On RHEL 5.2, I can't do various bundler-related things under "rvm use 1.9.2-p180@rails". works fine under "rvm system". Where should I look for cause?

Example:

% rvm system
% gem install bundler # works

% rvm use 1.9.2-p180@rails
% gem install bundler

ERROR:  Loading command: install (LoadError)
    no such file to load -- zlib
ERROR:  While executing gem ... (NameError)
    uninitialized constant Gem::Commands::InstallCommand


Google led me to stack overflow:
% yum install zlib zlib1g zlib1g-dev # googled advice, for ubuntu
Package zlib - 1.2.3-3.x86_64 is already installed.
Package zlib - 1.2.3-3.i386 is already installed.
No package zlib1g available.
No package zlib1g-dev available.
Nothing to do

Since it works under "rvm system," this doesn't seem compellingly explanatory,but maybe?

OK, some progress: under 'rvm system', irb can find zlib, but under "rvm use 1.9.2-p180@rails" it can't

ruby-1.9.2-p180 :001 > require 'zlib'
LoadError: no such file to load -- zlib
from /usr/local/rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in require' from /usr/local/rvm/rubies/ruby-1.9.2-p180/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:inrequire'
from (irb):1
from /usr/local/rvm/rubies/ruby-1.9.2-p180/bin/irb:16:in `

'