text display problem in mail

[glenlee@life-in-christ.holiness.ch]

When I receive text mail, or try to compose mail in text mode instead of
html mode, some key combinations appear to add a tab between the
characters.  For example, the word "subscribe" will display as:

subscr          ibe

This is happening in Evolution and Squirrel mail (the only 2 I've tried)
regardless of the desktop I'm using.

I'm using Lenny Stable on a Dell desktop.

Suggestions?

Glen