Not sure what setting I messed up... I remember AFC working (face detect, center, etc) with my 14-140 when I first got the camera, but never really used AFC after that forgot about it while I festively changing every setting during investigative tweaking.

Anyway, now that I have my swanky 12-35, I was re-exploring AF capabilities... and I can't get them to work at all unless I half-press the shutter button.

Any ideas on what I've bunged?

If you go into the menu and scroll down to the motion picture sub-menu, there should be a 'Continuous AF' option on the second page - have you turned it off there perchance?

Thanks Craig... that option was checked.

Discovered the root of my problem, and it's fairly simple: I'm a nincompoop. Apparently (and logically) it will only continuously autofocus whilst recording... so it's always worked fine, I've just forgotten how it works and didn't test the simplest bit until now.

So yay for that