While playing a newly generated world, I was flying over a hill when I was suddenly stopped in mid-air as if I had hit an invisible wall. I was able to maneuver around the point and found more blocking points that seemed consistent with the overall pattern of the nearby terrain.

I then generated another world, and shortly after I started flying around I encountered a jungle with half-generated trees, and upon flying near one where the missing half should be, I encountered more "invisible terrain". In fact, looking around I noticed more terrain generation bugs, such as strips of missing snow in the nearby taiga. I was able to make missing terrain re-appear by attempting to place blocks where the missing terrain should have been. It's almost as if this is a BUD-related issue (in attached screenshot, the log at the bottom center appeared when I tried to place grass there).