I just found a bug, which has already been fixed in the 1.4 release. Although it is fixed, I thought I'd bring it up. I believe it was related to the loop_context_vars problem in that when you had an empty loop, and then used that loop within a template, you got unpredictable results. In my case there would be 1 or 2 empty iterations of the loop. Upgrading to 1.4 fixed it.
Yup, I'll verify that that was indeed a bug in the 1.3 release. Now, the big question, did you try the shared_cache stuff? Did ANYONE try the shared_cache?