I caught this completely by accident. I was designing a MEGA shield for a client and have never used many pins on the shield. Lately we started moving pins around to reserve pins for SD card and other possible accessories, which is when I found the problem:
I've highlighted pin D22 in the schematics and have it next to board view, or have I highlighted pin D52 instead??!!
Conclusion: a total of three headers are flipped or rotated 180 degrees. This includes D14-D21, D22-D52, and D23-D53. I am just showing one of them. If you really want to start a MEGA shield design with sparkfun design, make sure you flip them back.
Besides this, the bottom left screw hole should be moved 0.05" to the left to fit the corresponding hole in MEGA2560 design.
Seems like someone before me found the "flipped header" problem:
Search for member #230598. I wish I read it before.
While attempting to make a corrected version of their design, I also found a bunch of stray wires coming out of almost every pin header. Delete those too if you want to use the design.
No one ever said that "Open Source" had to be accurate... Come to think of it ... that's one way to keep your own designs 'closed'... Build some errors into it..
Now I have to check everything before I trust another designer. I thought Sparkfun was trustworthy but their credit rating just fell a few points on my book :)
John, I learned a long time ago not to sign my name until I checked every square inch... of Every board I ever worked on, my designs and others especially.
Got it Bob. This is the first and last time I'm using someone else's design.