Imagine simple css:

@charset 'utf-8';
@media all {
body {
}
body {
background-color: gold;
}
}

compress it:
java -jar yuicompressor-2.4.2.jar sample.css -o sample-min.css

result:
body{background-color:gold;}}

expected:
@charset 'utf-8';@media all {body{background-color:gold;}}