Huge number of repeated image download requests from Photon

Hi,

I host a WP instance which has Photon turned on in Jetpack for CDN delivered images. I am seeing a very large number of repeated image requests from Photon to the blog which is taking up huge amounts of bandwidth. For example, from a randomly chosen single daily logfile, Photon is downloading 3.6GB of images, which covers only 468MB of data (there’s a huge amount of repeated requests) – this is about 80% of the total server bandwidth – and these requests are happening on a daily basis.

Log excerpts like the following are especially concerning:

192.0.99.34 – – [31/Oct/2015:13:50:34 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”
192.0.86.129 – – [01/Nov/2015:03:40:11 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”
192.0.86.185 – – [01/Nov/2015:03:40:17 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”
192.0.86.162 – – [01/Nov/2015:03:40:20 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”

<snip another 140 requests for the same file…>

192.0.86.143 – – [01/Nov/2015:03:47:35 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”
192.0.86.125 – – [01/Nov/2015:03:47:38 +0000] “GET /wp-content/uploads/2014/11/IMG_1667.jpg HTTP/1.1” 200 500600 “-” “Photon/1.0”

What is going on here? Why doesn’t Photon download it once, then check to see if it’s changed? (or at least download it once, and not do repeated downloads from different servers over and over again?) I thought the idea was to save bandwidth on servers by CDN delivery, not to have Photon chewing through bandwidth on its own!