How do you know that's a "magic byte"?
In one of the projects I lead, the programmer used an 80-byte end-of-file terminator. The chances of finding that exact terminator in a fixed-length record is very small, no? He thought so. He was wrong. It only took a few months to happen and it brought the system down. The dumbass forgot that his source code had the EOF record in it. There wasn't usually any reason to ship his code through the system but sooner or later he did and it got aligned just "right".