Basically a renotify of Blueprint: Create an interface function with no return value and it doesn't get copied to class blueprints that add it. - UI - Epic Developer Community Forums
as of 4.7 Preview 5, this problem still seems to be present. Wasn’t sure if it was different then his.
I didn’t see it on fixed/known blueprint bugs on 4.7 preview page
Create blueprint X
Create blueprint Interface Y
Create function Z that has no input/return (just a simple function call)
Add interface Y to X. And Z doesn’t appear in list (however it can still be called, but no way to implement it)
If I have other functions, that have any number of inputs/outputs, it does appear in list. Thus only solution is to have all my void functions have a input or return that I don’t utilize.