lessphp filter ignores @import statements

https://github.com/kriswallsmith/assetic/issues/109

in app/config/config.yml…

assetic:
    debug:          %kernel.debug%
    use_controller: false
    filters:
        cssrewrite: ~
        lessphp: ~
        yui_css:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"
        yui_js:
            jar: "%kernel.root_dir%/Resources/java/yuicompressor.jar"

in *.html.twig…

{% stylesheets
    '@BppCoreBundle/Resources/less/bootstrap/bootstrap.less'
    '@BppCoreBundle/Resources/less/core/*.less'
    filter="less,?yui_css"
%}