Washington: Cornus 'Venus' Problems

Hi all,
I am a newbie to this fine community. I am an experienced gardener. I am wondering what the group experience is with Cornus 'Venus'. I got a couple for my garden when they first started coming available. At first they were fabulous. However both trees, one of which is six years old the other 5 years old, have started a serious decline. The leaves turn red and fall off just like it was fall. One one tree the condition started while it was in bloom. There appears to be no spotting or other problems with the leaves. Some of the branches are completely defoliated. The cambium remains green. These trees are getting watered regularly and I wonder if the hybrid has inherited Cornus nuttallii's dislike of summer watering. They sure looks like one I managed to kill when I turned a dry bed into an irrigated one some years ago. I have Cornus florida, Cornus nutallii, Cornus 'Eddies White Wonder' growing in various spots in my garden in zone 7 Stanwood Wa. The others trees are doing fine, except I lost one Cornus nutallii which failed to leaf out this spring. I also lost 4 magnolia's which I may discuss in a separate post.

What are other people's experience with C x Venus? Any idea as to the problem?

Thanks
Mike