Thanks Rob,
I posted here because it is a development issue. I'm developing on one system and testing on another. If they don't behave the same, then I have a problem.
The link you provided is for Windows 7 and Vista. It appears that there is no Microsoft Camera Codec Pack update for Windows RT 8.1 (at least not yet). I've been unable to find out if there was one for Windows RT 8.0. The funny thing is
that I didn't load a Codec Pack for my iMac's Windows 8.1 installation either, yet it works fine there. I just expected core functionality like software codecs to be platform independent, so I assumed I was doing something wrong setting up my development systems.
Anyway, thanks for your help.