Graphics move when adding filters

Question

I'm having strange things happen when using graphics.
When I add a filter eg GausBlur my graphic moves down when adjusting blur. I also get this when I apply other filters as well, but usually when I add a second filter/plug to the graphic.
I'm on a macpro dual quad, 16g ram and all apps are up to date
Cheers

Answer 1

The graphic shift has nothing to do with Blackmagic--that's a bug (or at least an issue) with Premiere itself.
It's pretty simple to replicate. Plop a Drop Shadow effect on a title (or other alpha graphic), followed by a Gaussian Blur (or Fast Blur) effect. You can first see the shift just by swapping the order of the effects; they can be left at detent, and simply changing the relative positions of the effects will cause the graphic to jump.
If Drop Shadow is above Gaussian Blur in the effects stack, even with GB set to 0, changing the Softness parameter of DS will shove the graphic down and to the right.
If Gaussian blur is above Drop Shadow in the effects stack, even with DS set to 0, changing the Blurriness parameter of GB will shove the graphic down and to the right. However, in this case, you can mitigate that negative effect by ticking the Repeat Edge Pixels option in GB. No matter what you move, the graphic will stay where it should. This doesn't work in the other scenario, however.
My understanding of this--though I'm not sure whether it's a bug or a functional limitation--is that when you're adjusting these softness parameters for either effect, you are altering the clip's dimensions via the alpha channel. That's why ticking the Repeat Edge Pixels option stops this; it clamps the alpha channel to the original image's dimensions. As you adjust these parameters, the alpha channel's dimensions bloom/grow larger, and this changes the clip's anchor point, causing the shift.
Obviously, this isn't right, no matter how you slice it, but I suspect that simply saying it's a bug is not really getting to the heart of the matter. I imagine there are some larger underlying issues with the way Premiere Pro handles alpha channels and effects that manipulate them that would have to reworked first. In other words, this is probably not something you'll see in a point update; it will likely require a new version of the software to see a true fix.