Strange case sensitive problem with autoload own libraries

Try to load a library 'MY_Userbundle.php' with
the autoload config.

The class name of 'MY_Userbundle.php' is 'class MY_Userbundle' .

When i do this in my localhost with :

Code:

$autoload['libraries'] = array('my_userbundle');

everything is fine,  but if i try this on my productionserver,
i get this error:

Unable to load the requested class: My_userbundle

when i change on production server to :

Code:

$autoload['libraries'] = array('MY_Userbundle');

everything is also fine.

Im working with the prefix 'MY_' and when i rename the MY_Userbundle.php
into Bundle.php and also renam the class MY_Userbundle in  class Bundle and
than do this in config_autoload :

Code:

$autoload['libraries'] = array('userbundle');

everything is also fine.

Why my local settings don't run on the production server?
What is going on here?