Jetpack Photon not working for header in 2.3.3

After updating to the most recent version of Jetpack, Photon no longer serves the @2x image of my header and header background. So they now look blurred on Retina devices. They were pin-sharp until the update. How come? I’m using a StudioPress child theme with Genesis. Nothing has been updated or added other than the Jetpack update.

As per the Jetpack website:

Makes the thumbnails Retina / High resolution display ready (by devicepx.js, only with Photon) – up to a point where the original image has a resolution high enough.

It was working until I updated. Other images are unaffected.

The code I use for the header and header background is:

@media only screen and (-webkit-min-device-pixel-ratio : 2),
only screen and (min-device-pixel-ratio : 2) {
.header-full-width #header .wrap {
background-image: url(images/[email protected]);
-webkit-background-size: 310px 86px;
    }
}

@media only screen and (-webkit-min-device-pixel-ratio : 2),
only screen and (min-device-pixel-ratio : 2) {
#wrap {
background-image: url(images/[email protected]);
-webkit-background-size: 440px 66px;
    }
}

I can’t show you a URl as the site is not ready for release but, as I say, everything was working until the update, with the header and header background looking pin-sharp on Retina devices. I haven’t changed anything.

Any help would be awesome.

Cheers.

G