Hi James,
Thanks for providing the assets and additional information. I was able to load them up and take a look and it appears to be functioning correctly in our internal build. Please look for the adjustments in an upcoming Rocket release.
Regarding the UE4 preview being completely blacked out on some nodes due to the negative values in the panners, our developers have indicated that this is an intended change from UE3 as in this situation they were not accurately representing the preview values correctly. Since there is no good way to visualize negative values, we display them as black instead of display an incorrect preview.
Thanks!
-W