it depends on who the center is. If a QB works with a center for a long time, it should never happen. However, when you are receiving snaps from a center you are unfamiliar with, it takes some adjusting. The ball comes in perhaps a bit quicker or later than it did with the other guy, and perhaps at a different angle. However, they are inexcusable when they happen in the game.
The ones with Grossman during the past seasons were obviously his fault. Anyone with half a brain could see that he was jumpy and pulled out too early. When you have a QB-C combo of Rex and Olin that have worked with each other all through training camp, and the season, they should never, EVER happen!