background-image not visible in Safari (ipad)

[Nick]

On my site, I have a button with a background image set in css. It works perfectly in all browsers I checked, except on my ipad (safari, ios 9.3.1).

The css looks like this:

#mapsearchbox input[type="submit"]
{
    background-image: url("../img/searchbutton.png");
    width: 19px;
    height: 19px;
}

Cassette rewrites the url, as mentionned in your doc (http://getcassette.net/documentation/v2/stylesheets) so that it is served from the root.
I think this is what is causing my issue. If I move the background-image property to inline css in my html page (which means the url won't be rewritten), it solves the issue. Seems like Safari does not like the rewritten url to the image...

Thanks for helping.

[Nick]

Final test, I grabbed the path to the image rewritten by cassette and it looks like this:

http://my.ip.address/cassette.axd/file/content/img/searchbutton-be255ea878244b48a29e90a250c37a23f9247892.png

If I type it in firefox on my computer, I get the image.
If I type it in safari on the ipad (paste to ensure no typo error), I get a "server error - 404 - File or directoy not found".