Views Cycle

We've just solved a highly perplexing issue on a recent project.  Mysteriously, our lovely transitions on a Views Cycle banner rotator were not happening in IE7 and 8!  Instead of smooth dissolves, the images transitioned suddenly with no effect.

Sounded like a javascript issue, maybe a conflict? But Darko disabled each one by one, and still no solution. He did notice that the transitions worked beautifully by switching the theme to Garland, so something in our custom theme must be mucking things up.