No, unfortunately that works. You can use it to charge a device and plug in headphones at the same time. :-(
I was also looking for an adapter to charge two devices at the same time, so if you have any tips...

I've tried all combinations with iphone, ipad and headphones for charging: it only ever charges on one socket (funnily enough, it doesn't matter whether the one for charging or for the headphones is used for charging).
The simplest solution is probably a cable with multiple plugs (with the correct cable specification!) ...