My 35 Art was wonderful about 90% of the time, but had 'bad days'. When it acted up, it would front and back focus without reason. Similar to what has been described in some of the reviews written about the 50 Art. But, my copy of the 50 Art is stellar in AF consistency. Up to about 15-20 feet, it's perfect. After that it's not right and I'm sure a dock could fix it for me, but in the 2,000+ shots I've taken with this lens, I've only shot at 1.4 past 20 feet two or three times. Given how well the lens works for what I do, I don't want to mess with the dock.
Because I have had issues with (multiple copies of) the 35 Art, I understand the frustration of inconsistent AF (inconsistent, not just always front focusing, or always back focusing - which is easy to fix with AFMA). My experience leads me to believe that there may be copy variation in the lenses. I seem to have found a great one and am really pleased. But, I do want to reiterate what I wrote a few posts back; When I first got the lens and shot static 'test' objects, under backlit or low contrast conditions, the lens appeared to be inconsistent. However, using this lens in the real world with clients and my kids (my kids move quick) this lens is just as consistent as my L lenses.