The 50 has a Focus shift!
I've noticed that, but its minimal. In fact, in inconsistency of focus is much greater than the focus shift.
I've played with two copies of the 50/1.4, and I'm happy with the lens I've got. Both were the same. Mild focus shift, not too bad, always away as you stop down. I've been told.. not sure though, that this is due to the placement of the aperture blades in the optical path, not being exactly - EXACTLY - where they should be. Supposed to be a not uncommon "fault" with fast lenses using (more or less) Gauss designs. I know the Leica 50 Noctilux suffers from focus shift, and the rangefinders must be re-adjusted if you plan on shooting mainly wide open. You match a body to a lens, and to aperture wider than f/2.0 with Leica M's. Focus shift is not uncommon.
The main problem I've seen, is focus inconstancy with the EF 50/1.4USM. Mount the lens on a camera, camera on tripod. Shoot at a newpaper at more or less 2 meters. Shift the lens to infinity before focusing. Shift the lens to closest focus before focusing. Do that about three sets of images. Shoot at f/2.0 and you'll see what I mean. The lens, the mechanism is just... inconsistent.
I like the lens. I just know that close distance at very wide... say wider than 2.8 is gonna be an issue. At farther distance, say, stage distances - when shooting a band - its fine at f/2.0 for sharp images in the center. Shoot it at f/1.4 and the whole affair gets a little low contrast. All 50/1.4 lenses do that... the Canon is no exception, nor is it the oddball. If you want a sharp lens wide open at f/1.4 shoot a 50 Summilux 1.4 from Leica. Those do amazingly well.