Demonstration of how a single action allowing for client code to send in actual callbacks for job execution.

gears-test.php

<?php
/*
  Plugin Name: WPGears unique bug proof of concept
  Plugin URI:
  Description: Hit any page with a `?do_job_test=1` param in the url and then check the options table.  If you DON'T see
			   "random string maybe not" in the option then that proves the bug.
  Author: Darren Ethier
  Version: 1.0
 */
/**
 * Demonstration class that wraps WPGears implementation so that client code can send actual callback to be used.
 */
class WPGearsAdapter {
	public function add( $callback, $args ) {
		$args['job_callback'] = $callback;
		//$args['make_unique'] = true;
		wp_async_task_add( 'wpgears_bug_test_callback', $args );
	}

	public static function doJob( $jobData ) {
		//grab the registered callback from the jobData
		if (
			isset( $jobData['job_callback'] )
			&& is_callable( $jobData['job_callback'] )
		) {
			//remove callback from jobData so it isn't sent to the callback as an argument.
			$callback = $jobData['job_callback'];
			unset( $jobData['job_callback'] );
			return (bool) call_user_func_array( $callback, $jobData );
		}
		return false;
	}
}


//set action for wpgears async request
add_action( 'wpgears_bug_test_callback', array( 'WPGearsAdapter', 'doJob' ) );

add_action( 'plugins_loaded', function() {
	//sample jobs getting added in test kicked off by get
	if ( isset( $_GET['do_job_test'] ) ) {
		$adapter = new WPGearsAdapter();
		$adapter->add( 'gears_option_update_test', array( 'value_to_use' => 'random string' ) );

		//add another job for different callback and different values.
		$adapter->add( 'gears_option_second_update_test', array( 'value_to_use' => 'maybe not' ) );
	}
} );

function gears_option_update_test( $value_to_use ) {
	$existing_value = get_option( 'gears_option_test', '' );
	return update_option( 'gears_option_test', $existing_value . ' ' . $value_to_use );
}


function gears_option_second_update_test( $value_to_use ) {
	$existing_value = get_option( 'gears_option_test', '' );
	return update_option( 'gears_option_test', $existing_value . ' ' . $value_to_use );
}