Yesterday I was asking this question:
But now I have the problem, that there is no transparancy of blue image (black50.png) to the feature image anymore, how can I bring back the transparancy?
You have to wait a little while, then you can see the seconde slide it's an image, with blue box on it, the blue box should be transparent.
What browser you are using?
It could be only browser problem, or clear your browser cache..
I can see the transparent background, I attach you the screenshot.