Distortion of TIFF images

This may not be the right forum for this question, but I figure that denizens of this area may know something about TIFF files that will help.  The question is, why do some TIFF images seem to foreshorten in the Y direction when displayed, edited, or copied?

Example: I send and receive electronic faxes using a service provider, and they look fine and print fine in a TIFF viewer.  If I edit faxes I have received (add annotations, etc.), save, and re-fax to someone, they are distorted.  If I print from the editor to PostScript or PDF, the result is not distorted, and can be re-faxed without problems.  My fax service has a cryptic note in their FAQ that "some TIFFs may produce unexpected results," which leads me to believe that the file format itself may have some issues.

The TIFF editor in question is the one that Microsoft supplies with Windows 2000, which apparently originally came from Kodak.  In all fairness to MS and Kodak, though, I have seen very similar things happen to TIFFs on Linux systems using completely different tools.

Is there a "TIFF for Dummies" page or something that might demystify this issue for me, or can someone help out?

Thanks

Justin Harlow