It's definitely a real bug as I had the same problem. If you're willing to read a not very coherent bug report that I basically kept adding to as I tried to debug the problem, you can do so here.
https://code.google.com/p/googleappengine/issues/detail?id=7167 I notice similarities in the code. I was also using set_multi_async. Interestingly, in your code, it hangs before you even call get_result on it. Maybe you cannot stuff the memcache pipeline with too many pending async requests. In my code though, I had only had two such requests. I have since completely rewritten the code (using ndb with its automatic memcaching), so I don't know what caused it. I had sumed it up in the bug report like so. "This shouldn't be happening but it is!" -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To post to this group, send email to google-appengine@googlegroups.com. Visit this group at http://groups.google.com/group/google-appengine. For more options, visit https://groups.google.com/groups/opt_out.
