Disabling WorldFrame:SetPoint in nUI.lua does remedy the problem, but, and with no offense to Scott nor any other addon author using viewport mods, Blizzard needs to step up and actually fix this, instead of beating around the bush, and pretty much placing the blame on the addons being used.
I've been following the threads pertaining to this on the WoW forums, and what it pretty much has boiled down to, in spite of users making the effort to link discussions with addon authors regarding this NOT being an addon issue, but instead, a problem with the way the aforementioned function is being implemented by Blizzard, is simply this: Since disabling your addon makes the problem go away, there is no problem to begin with.
Can't say as how I am surprised by this, honestly. I can, however, applaud the time and patience put forth by those authors who have to deal with this sorry attitude.
Edit: I R gud speeler