Ah, thanks Chappie. I hadn't realised that it loads both.
Re the 20:20. Those with the leading-edge retina devices will demographically be those with the best eyesight :-) (And it's not so leading edge any more, now that we have cheaper 4K screens coming through.)
Doing some more digging, this seems to be a WordPress bug, not a Customizr bug. On the second page of this post, there's a WP hack:
I got the same problem after upgrading WP from 3.6.1 to 3.8.1.
It looks like there was a change in wp-includes/media.php function wp_constrain_dimensions(): width and height is set to max(1, $current_<w/h> * $ratio). I have changed:
$w = max ( 1, intval( $current_width * $ratio ) );
$h = max ( 1, intval( $current_height * $ratio ) );
$w = intval( $current_width * $ratio );
$h = intval( $current_height * $ratio );
as it was in v3.6.
It's a hack rather than fix, so do it at your own risk.
I don't see how it works because the 3.8 code looks fine to me. I could imagine that the new code might be bringing out another bug somewhere else, though—for instance if the image size was in some way discarded previously as it was malformed or unobtainable, but constraining it to a max fixes it totally and incorrectly to 1px.
Alternatively, the first page of that post says it might be a permissions issue. Can anyone investigate this permissions issue?
Maybe it's a combination of permissions (which refuses to give you the image size info, yet allows you to display the image) and the new code (which in the absence of the image size info constrains the image to 1px x 1 px).
Sounds like a plausible scenario. Any WordPress image gurus out there?
Mods: any chance you could raise this to an image specialist's attention?