It seems the issue is perculating to the surface again, and employers are slowly becoming wise to the fact that often those seeking certification are those that don't have skills and real-world know-how in the first place.
Last time we saw code that didn't run on OS/390. It will throw an error while executing on OS/390 (aka z/OS, aka MVS), but not on UNIX, Linux (including on z/Series), or Windows. The problem is pretty simple:
newlines, or the chr(10)'s in the code
Some of the younger readers might be asking, "But why?"