Hello Rob,
I’m very sorry to hear you’re having this problem. I will look to see if it is a logged issue that other people are having. In the mean time, have you tried increasing the PHP memory of your site? Here is an article on it: http://www.dailyblogging.org/wordpress/increase-wordpress-memory-limit/?
Also, does this happen to you when reverting to the Twenty Eleven theme? You may need to set up your site on a testing environment to see if this is the case. I just want to make sure there isn’t a conflict there.
I will keep looking into it – thanks for reaching out!