Puzzling image drift

[John Vokey]

I have a stack that presents a series of disk-based images by replacing 
the file name of the image object on the card.  The images are not the 
same size, and over images the object appears to drift up and to the 
left.  As this effect does not happen with identically-sized images, I 
suspect it has something to do with how MC determines the location of 
new image when replacing the previous one of a different size.  I had 
assumed that the loc (top-left) of an image object was fixed, and all 
subsequent images would be displayed using that loc, but apparently 
not.  So, what gives?  MC 2.4.1, Mac OS 10.1.2.

John R. Vokey