Scrambled class name passed to spl_autoload_call via call_user_func

Question

I have discovered interesting behaviour of php while calling different classes dynamically. For some reason class name get scrambled and its look like slice of hashed string.

here is example of php code I'm trying to execute:

call_user_func(array('app_event', 'arrayItems'));

Here is backtrace of this event:

Array
(
[0] => Array
    (
        [function] => autoLoader
        [class] => init
        [type] => ::
        [args] => Array
            (
                [0] => j7ltlqmoy
            )

    )

[1] => Array
    (
        [function] => spl_autoload_call
        [args] => Array
            (
                [0] => j7ltlqmoy
            )

    )

[2] => Array
    (
        [file] => /site/class.app.php
        [line] => 107
        [function] => call_user_func
        [args] => Array
            (
                [0] => Array
                    (
                        [0] => app_event
                        [1] => arrayItems
                    )

            )

    )
 ...
 );

Can anybody explain what em I doing wrong and what can cause sting app_event to be translated in to j7ltlqmoy?

UPDATE

Script does work on all other classes and throws this weird text only when requested method is not implemented. I have managed to make my application work, however it still does not explain why does it scramble names instead of throwing error?