For JPGs with my K10D I set the WB to 5500 K to make sure the RGB channels are all at unity gain. (and best dynamic range for all channels!) If you shoot in overcast conditions with Auto WB the Red channel will get boosted and will probably clip depending on the scene elements.
For RAW I do not attempt to correct WB in ACR , but just tweak exposure controls if necessary. I never use AUTO. I use selective Hue and Saturation & Level controls in CS3 to straighten things out as required.
You can also help avoid blowing out the red (or blue) channel by keeping the camera set to 5500 K and then use a filter on the lens to correct the color temperature. I think many pros prefer this method.
The following filters are useful for overcast days or shooting in open shade ...
81A pale orange Warming filter to increase the color temperature slightly
81B pale orange Warming filter, slightly stronger than 81A. The opposite of 82B.
81C pale orange Warming filter, slightly stronger than 81B, opposite of 82C.
81D pale orange Warming filter, slightly stronger than 81C.
81EF pale orange Warming filter, stronger than 81D.
I too still have my A2.
Do you have any examples you could post of your problem images?