Yes, I’ve noticed that on mine. The versatility of that lens at its price point comes with compromises. It’s good for a lot of things, but great at none.
5D II, 7D, 40D, 20D (IR)
28-300 f/3.5-5.6L, 35-350 f/3.5-5.6L, 70-200 f/2.8L, 70-200 f/4L IS, 200 f/2.8L, 135 f/2L, 100 f/2.8L, 24-105 f/4L IS, 85 f/1.8, EF-S 17-55 f/2.8 IS, EF-S 15-85 f/3.5-5.6 IS