That example worked fine for me, the second example (a variation on the first) worked as the article described. Once foo() was "code", I couldn't update it (at least I couldn't discover how to do so outside of killing that bit).
I'd bet the first example didn't work at some point, and then was quickly patched.
The second example worked correctly seamlessly for me as well. I can easily edit text inside a code block in the WYSIWYG editor. Maybe they just patched that too?
Hmmm... possibly testing a patch... I still can't get it to work and checked for updates before trying. There could naturally be a difference in our sequence of steps, too. Once "foo()" is entered and detected as code, I can't add "bar." after the fact. I can add new code text in the middle of the detected code.
I'd bet the first example didn't work at some point, and then was quickly patched.