From the screen print, you used a new local adjustment and then made pick of the blue color within the layer.
On the selective color adjustments, they can be tricky, especially in a situation like you have shown, where the blue sky is coming against a green/yellow object. The issue I believe is the the blue color spectrum is very broad and you have to make sure you pick in an area very close to the branches, but that is still blue. If you don't then you can get the artifact issue which is a form of haloing due to the fact that the all the rest of the blue in the sky was darkened except for the area next to the trees. This effect will often not show up until you look at the image at 100%.
I think that you can resolve it by going back to the layer you created, then zooming in past 100% and then trying to get a color selection very close to the green. Judge the color you pick in the box that shows the selected color as many times I will not look at it and just try to work the color. The selected color box will let you know if you were closer to getting a match. You will have to get right next to the branches.
You can also attempt a tweak to the hue of the blue to see if this helps.
I couldn't tell if you shot the sky with a CL-PL or not, but sometimes that can help in situations like this by making the blend line between the tree and sky a bit easier to work with.
I feel that overall the Phase One color selection tool is superior to how LR does color adjustment and tend to lead with this tool first. But there are times you run into situations where it take a bit more work.
As of Phase One's support, this is a classic area where I feel a phone call would be a better way to work out the problem. With them working the same file with you and showing you how they fixed the issue. When I run into such a situation, often times I will contact my dealer first, not sure if that will work for you. Phase One as most companies now, has moved to the non human phone contact tech support. Phase has always been like that at least for the last 10 years. I understand where this model works, but many times a simple phone call can also get the issue fixed faster, as so much can be lost in email tech support transactions. I just finished a problem with Drobo that lasted close to a month that I still feel could have been fixed with a simple one to one phone conversations. But I am over 50 and old school. I believe Phase does expect the dealer channel to pick up a lot of this type of support.
You can send me a copy of the file if you like and I can try to work it up.
Paul Caldwell email@example.com