Core

There is a difference of ordering for js files, in case they are compressed / concatenated or not.
Looks like pagerenderer inverses the "forceOnTop files" while the ResourceCompressor doesn't.

if ($properties['forceOnTop']) {
    if ($properties['section'] === self::PART_HEADER) {
        $jsFiles = $tag . LF . $jsFiles;
    } else {
        $jsFooterFiles = $tag . LF . $jsFooterFiles;
    }
} else {
    if ($properties['section'] === self::PART_HEADER) {
        $jsFiles .= LF . $tag;
    } else {
        $jsFooterFiles .= LF . $tag;
    }
}

Instead of prepanding the file we should use the same logic as in ResourceCompressor. We should build arrays for each kind of section and merge them at the end.

The change of order should be communicated on launch. That's a breaking change for JS developers. They have to check the order of there JS files.