i was not sure whether to post this or not, but while i was wandering around in the CI 2.1.0 code, i stumbled on the library method of Loader core system class.
the library method of system/core/Loader.php is defined as :
public function library($library = '', $params = NULL, $object_name = NULL)
later on, at line 200 i found this recursive method call :
foreach ($library as $class)
so, it seems that the optional third parameter $object_name is not included in subsequent recursive method calls.
as i am not familiar with the code in such detail to decide if this is intentional or not, i want to point your attention at what i have found out.
This is by design, so that it can handle an array in $autoload['libraries']. Plus, you can't give all of the libraries the same object/property name.