It happens, I've seen it. I didn't think this would be a problem until I saw it happen in person, but it does happen, occasionally. I've seen it on two bikes in three years in our shop. It certainly isn't a problem on all of these "mismatched" situations, but if it does happen you CANNOT get the front shifting to be reliable, the "floating" will occur intermittently no matter what you do, no matter what you adjust. In the two cases in our shop, switching to cranks designated as "ten speed" solved the problem immediately. It can actually be dangerous if it does happen, because when you shift to the smaller ring and the chain doesn't engage the chainring......it can hurt.