1. I resolved WPPA slideshow over primary menu problem by adding codes to child theme, not by change z-index in Ubermenu (it did not work when I changed z-index to 80 there):
.main-content {
position: relative;
z-index: 1;
}
This may help some other people to resolve this issue, at least it works fine for me.
2. The fully featured slideshow still not working properly in my current working website with twenty fourteen theme. It works well when I reset firefox, but once I loged in wordpress admin, the problem comes back. I repeated this test few times, and did not resolve this problem. I am quite sure it is caused by plugin conflict in my website where quite a lot plugin installed, because in another test website where also twenty fourteen theme used (only 11 basic plugins installed), there is no such a problem.
Thanks
Z.G. Yang