I hadn't upgraded. However I just now thought of the most likely reason - it is possible (and indeed probable given you can't replicate it) I switched libraries in between, from a library that had no custom text columns to my test library that does? I can't remember doing that, but then my memory ain't what it used to be... sorry dude, hope that explains it.
I double checked my laptop which I haven't fiddled with these settings on and the custom columns appear in the list, so that confirms all seems to be working as it should. Sorry for wasting your time, should have thought of this reason before... too many things going on, brain hurts...
