That's the message you get on a patched machine. However, the patch is not sufficient: https://news.ycombinator.com/item?id=8365216 .

So from what I can tell, neither my Raspbian or Ubuntu setups have this second vulnerability properly patched yet (although they have the first one).

I guess I'll just have to wait until it becomes available. They're usually pretty responsive about issues like this.

Or an earlier version of bash (4.1), which I'm assuming (haven't installed any patches within the last month on a centOS6 machine) hasn't got the issue?

If you see that "ignoring function definition attempt" message you definitely have the first patch applied (but not necessarily a fix for the second problem) That diagnositc was added by the patch itself. See http://ftp.gnu.org/pub/gnu/bash/bash-4.1-patches/bash41-012

Maybe you have auto-update turned on and didn't realize it?

It has, there is a patch for bash 4.1

ftp://ftp.gnu.org/pub/gnu/bash/bash-4.1-patches/bash41-012