302 caching?

Hi, I've been using the large_thumbnail option and have come into a problem with what I can only presume is caching.

Occasionally when I modify a URL from: http://i.imgur.com/5hFoN.jpg  to http://i.imgur.com/5hFoNl.jpg 

I get the http code 302, with no redirect link. A simple way to get around this is to wait 100ms or so and try again. I presume in this time, the image is cached to the smaller thumbnail format.

Is this expected behaviour? If so, is my "fix" acceptable?

Thanks