just my 2¢
I've seen two behaviours. One is that if one crosses a munch segment that is outside the configured route, unless we give the client enough time to reroute there, it may not munch the segment. It does change to pacman, but the road doesn't turn white. I usually force routes ending or passing through the munchable roads to ensure the client knows I'm really passing them. Again, it's weird, because the client knows I'm on that road (the pacman icon), but if the route is nearby, it may not reroute through the segment and never white it at all.
Second, I've also seen a lot of cases where I munch away segments and the segments come back as munchable on the next mapdate. As I also see that some mapdates contains some changes but not other ones (even if they are done on the same day, or even before), I have a feeling that some data is lost / postponed / queued and may probably enter only on the next mapdate, as those roads are correct on the editor and hence I doubt the data was completely lost.
So just munch away again and again every two weeks until it's fixed. Too bad the prices of the fuel