Thanks to a mis-labeled board (it actually had an 8720 on it, rather than an 8722), I really got things screwed up.

And it turns out that MC's documentation is indeed correct - the 8720 has a block size of 8 bytes, while the 8722 has a block size of 64 bytes.

Everything is working now. I *would* let Darrel feed me some of that crow, but I'm a vegetarian !