Minify doesn't work (files are not created) @ HHVM nginx

Hi,
I’m using WordPress + W3 Total Cache + HHVM + nginx and minifying doesn’t work. The files aren’t written to the /wp-content/cache/minify folder. But it’s writeable and all other folders like /config or /tmp are created by the plugin.

I’m using the latest versions of all plugins.

Some images that could help:
http://gopeter.de/transfer/w3tc-1.png
http://gopeter.de/transfer/w3tc-2.png
http://gopeter.de/transfer/w3tc-3.png

https://ww.wp.xz.cn/plugins/w3-total-cache/