missing tech

[bc35]

I had a random event which allowed me to research Stormbringer. This is supposed to lead to Sky Diver. It did not. I was not worried because I thought other tech might be required also. But I have researched 3/4 of the tech tree now, and I have all the required tech according to several versions of the tech tree graph I have found. Is it a common problem? Is there a fix?