Title may be a misleading, this isn't directly Phalcon issue it appears, running the examples as shown here won't work on Windows 8, below is a simplified direct test, it just won't produce any output. If I try the command directly in the command line, I do get the compressed CSS file output.
$result = shell_exec('java -jar d:/yuicompressor-2.4.8.jar --type css --charset utf-8 main.css -o main-min.css'); // $result is empty
I've tried system() as documentation example shows, and exec() as well.
Is there some setting within Windows, Java exe or PHP that will allow this to happen, or is using PHP to execute a .jar file a dead end on Windows 8?