The change in clocking frequency
can have an impact on the load requirements (which you need to meet to prevent transmission line reflections). The change is usually in how strictly you have to adhere to the requirement, and less often a change in value. There are too many factors that come into play to say why one person's setup actually works in this situation...but suffice it to say that the effects of reflections on a working setup are small enough that they don't have an impact large enough to completely lose sync (you might however be encountering an undue amount of jitter and simply not realize it).
Everything from a tiny cold spot in a solder joint to a minimal amount of oxidation at the connection can have pretty drastic influences on the reflective property of the connection. It may be that Ed's setup is encountering these very difficult to narrow down elements, or that his system is simply more sensitive to transmission line reflections.
I found a little animated GIF that shows the effect reflections can have on your clocking...kind of anyway, but picture instead of a single pulse (as in the GIF) what can happen as additional pulses are sent WHILE the reflections are bouncing around:
http://courses.ncsu.edu:8020/ece480/common/htdocs/images/aa- xmission-trm.gif
Cheers,
Chris