Here you have, ;o)

[Me]

From: "Riad S. Wahby" <rsw at mit.edu>
> You have set your "View" options to include "Show extensions for all
> files."  This is not the default behavior of Windows since Windows95,
> so most people don't have this option enabled.

View->[X] Hide file extensions for known file types

If there is another option that alters this, or overrides it in OE5, I do not
know of it and have not changed it from it's default.