Hi there
Looking through this thread it would seem the "fix, if you will, is to create an image with a larger border that is rendered as transparent.
Just a guess on my part as to the cause, but I know with video editing applications that sometimes you have to be specific about the number of pixels wide. Odd things happen if that number is an odd number. Perhaps it's the same with these images in Captivate? If that holds true, it could also likely explain why the issue has "persisted" across several versions.
But that's just a WAG on my behalf. 
Cheers all... Rick 