Pentax 12-24 blue fringing

I have had my 12-24 for about 6 months, using it with a K100DS. It has become one of my favourite lenses.

Whilst I heard the occasional comment about CA and fringing, I didn't really think too much about it.

However, using the lens with my new K7 this week I took a few local landscapes with the 12-24 as test shots. When I brought them into Lightroom I could see severe blue fringing around a plantation of trees against a blue sky on the horizon. I mean severe. Admittedly, it was a very bright summer day, and the tree against sky is a classic CA problem shot.

Just out of interest, I took a couple more today with the K100DS+12-24. Sure enough, there was some fringing, but not quite as bad. Ok, it wasn't quite as bright, but the difference was noticeable. I took a few shots with differing exposures, and the fringing all but disappeared when I stopped right down until the shutter speed was about 1/100 seconds.

So is it possible that the K7 produces more CA? I guess the megapixel difference could have something to do with it. Also, is it expected that smaller apertures will reduce CA?

I did have the lens correction switched on with the K7, so I might try again with it off to see what difference it makes.