Matt,
I think I figured out what is happening. It all has to do with layering. If there are multiple images and a text box overlaps one or more of the images, the text box must be on the topmost layer for the "spread/trap" issue not to occur. If one of the images is on the top, then a text box, that then overlaps another image, the text will then "Spread/Trap" wherever the text touches the image area behind it. This only shows up when you "print" the slide. It doesn't show up on-screen. See if you can duplicate this.