I've taught the same class f2f and online in the same semester many times over. It's not as confusing as you might think. What's actually much more confusing is teaching two or more f2f sections on different schedules (like a MWF and TTh section). That's where I'm constantly getting the "Hey didn't I already talk about this?" thing going on.
I agree--I'm teaching the same class online and F2F this semester and find it much less confusing than teaching two face-to-face sections. It has been interesting to discover that the two classes have very different reactions to the material. I haven't noticed such a dramatic difference among f2f sections.