I wonder how widespread it is throughout the entire manga industry. I suspect it could be possibly more widespread than we think, and not an issue until someone get blatantly caught, like this case. The same thing happened to D.Gray-man author Katsura Hoshino, and they just put her series on hiatus. Granted when it came back it was never the same / as good.
I have seen the pictures where they line up the traces and they do match pretty closely. However, the artist can't have traced the entire series and the art is pretty consistently good otherwise. I think it came down to laziness, or saving time taking shortcuts to hit deadlines.
I really enjoyed the series, it's really a shame. At least it ended at a good enough spot.