Lance, I'm using X3b 64 bit with Windows 7 on an Intel Q6600. And, since this is a graphics related issue, I have an ATI 5450 graphics card.
I played around with it a bit, it actually happens with quite a few plugins and instruments, whether they are VST3 or not. I'm using the normal version of Ozone, by the way.
Here's a technical description of what I see on my machine:
If the width or height of the gui switched
to is smaller than the width or height of the gui switched
from, the light gray background is redrawn as if allowing for a gui about 1/8" larger than the actual dimension of the gui switched
to, leaving that 1/8" strip of the gui switched
from along the right and/or bottom edge of the gui switched
to.
Example: gui1 is 10" wide x 8" high; gui2 is 7" wide x 6" high. When switching from gui1 to gui2, the background redraw leaves a rectangle 7 1/8" wide x 6 1/8" high for gui2, then gui2 redraws a rectangle 7" wide x 6" high, so to the right and bottom of gui2 you see the 1/8" of gui1 that was not cleared by the background redraw.
When switching from a smaller gui to a larger gui, I do not see anything unexpected.
Hope this helps.