Yeah, so was I. There have been times the offset was caused by a change in ImageMagick. I don’t really recall the details, may I can find the related topics here. I know there is also an offset table/array too.
I think this is semi-related
http://imagemagick.org/discourse-server/viewtopic.php?f=3&t=28403
Granted now we’re talking horizontally instead of vertically