With my limited brewing experience, I can't offer much explanation on why you are getting sour notes, but I can tell you I haven't had any sour issues with using 05. I've only been brewing since Oct and have used 05 for 3 APAs, 2 IPAs, and 2 Milk Stouts and none of those had any "sour" issues. It will be interesting to see what is contributing those sour notes w/ your 05 batches.
On a different note, I recently brewed one APA with 1056 (with the same recipe that I used for one of my previous APA) and my friends and I really couldn't tell any difference between 1056 and 05.