I don't know why I keep getting unexpected results when I cycle from one image to the next.  If I currently have a 4 image viewport display, (for example displaying image01.tif, image02.tif, image03.tif and image04.tif) and then I cycle (using CTRL and left or right arrows, OR using the mouse) most of the time, cycling through an image in one viewport that is already displayed in another viewport makes one or the other viewport go blank.
 
This happens on a PC, 1.5GB RAM, IM 3.5.2.
 
It also happens on a Mac Powerbook G4, 1GB RAM, latest OS X, and IM 3.52.  In fact, I cannot work with imagemodeler on the mac, for which I purchased it, because the displays get all garbled, and show just a mess of pixels when I cycle or zoom.
 
What is the culprit for all of this?  What is the fix?