Warp stabilizer broken on flipped video
The warp stabilizer has a very basic bug: if you transform video by flipping it horizontally and vertically (i.e. the camera was upside-down), and then add a warp stabilizer after it, the warp stabilizer actually makes all the footage more shaky, not less.
The fix is to simply move the warp stabilizer to before the horizontal and vertical flips. After doing this, it works correctly. (Amusingly, the analyzing and stabilizing banners appear flipped now...)
Another clue is that the video does not need to be re-analyzed after moving it before the transforms for the stabilizer to work correctly. That suggests to me that the analysis is done without the transforms applied, but the stabilization is done with the transforms applied.
I'm using the OpenCL renderer on OSX with Premier Pro CC started in September 2018.
Durham Bell commented
This isn't isolated to a flip. Lots of effects will cause problems if they are above WS in the chain. Even the ones that shouldn't. For example: add a video Equalize above it and you'll get this weird kind of ghosting thing that happens (presumably it's sending part of it's output to the WS and part of it is bypassing it). It produces kind of a double image, or at least it does on every video I've inadvertently done it on.
Even weirder stuff happens if you use a fixed effect, nest it, then stabilize the nest. I was boggled about this one video that was producing a weird "letterbox" when there shouldn't have been any there. Turns out I had rotated a video 90 degrees, nested that, then applied some other effects and then nested that and applied WS over top of it all. That nesting or time, but not both has bitten me more than once.