After trying for more time than I care to admit I called Capture Integration in Atlanta where I bought my Phase One P40+ (after a great run with the P21+) and talked with Steve. No matter what I tried, I could not apply an adjustment to a click+shift group of images. The secret (to me at least) is that the small icon that looks like a stack of pictures has to be highlighted for group adjustments to be applied.
When you hover the arrow over it it says, " toggles between edit primary and edit selected variants".. this of course led me to believe that it was only for variants of a single image... not so. I have attached a few screen grabs. Using C1 really makes these files shine, but sometimes it is frustrating trying to think and work like the software. 
Thank you Capture Integration and thank you Steve... does make me feel better that I am not to first person to hit this wall.
Yes, as I explained to George, he is probably the 4th or 5th person recently who has called with this stumper. I honestly had trouble figuring out why this would be so important that it would be featured as a default tool so prominently. Until today, when I had selected about 10 images to look at them and compare each thumbnail and then I only wanted to process out the one I had selected as the primary variant. Instead of de-selecting all the images, I just clicked that toggle and hit command D to process that one out, even though all still showed as selected. In the event that tool is not important to your workflow, you can always customize the toolbar and just drag it off there.
Remember, in Capture One parlance, every file is a variant, even the original, as Phase One considers the raw file as a separate entity from everything you see in Capture One. Even the original raw capture is "represented" in some way, and as such, is still considered a "variant" of the raw. The "primary variant" would be the current selection - either as an individual file or as one of a collection, and would be indicated by the thicker white bar around the thumbnail. Yes, I also wish there was the ability to change that color or make it more obvious so it stood out more from all the selected thumbnails...
Steve Hendrix
