scroll-margin buggy on Emacs 21.1

[Jesper Nordenberg]

In GNU Emacs 21.1.1 (i386-msvc-nt5.0.2195)
of 2001-10-22 on buffy
configured using `configure --with-msvc (12.00)'
Important settings:
 value of $LC_ALL: nil
 value of $LC_COLLATE: nil
 value of $LC_CTYPE: nil
 value of $LC_MESSAGES: nil
 value of $LC_MONETARY: nil
 value of $LC_NUMERIC: nil
 value of $LC_TIME: nil
 value of $LANG: SVE
 locale-coding-system: iso-latin-1
 default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Setting scroll-margin to for example 5 doesn't work in Emacs 21.1. When 
moving the cursor down, the windows doesn't scroll until the cursor is 
moved off screen (it works when moving up). Emacs hangs when pressing 
page down (in CUA mode) when the last buffer line is just visible in the 
window. This only happens when scroll-margin is set to for example 5.

Recent input:
<menu-bar> <help-menu> <report-emacs-bug>

Recent messages:
Loading my-html (source)...done
Loading my-jde (source)...done
Loading autoinsert...done
Loading headers (source)...done
Loading c:/emacs/mylisp/my-main.el (source)...done
Loading cl-seq...done
Lisp hook loaded
Loading semantic-el (source)...done
For information about the GNU Project and its goals, type C-h C-p.
Loading emacsbug...done