I am again about the bug,

 From the Manual: "Taking forever to complete a command can be a bug, 
but you must make
certain that it was really Emacs's fault."

The following command make emacs taking forever to complete a command 
for all tested versions (21.x) up to ver. 21.2 ., that is the last I have.

PageDown from the start of the file of the exact lengths for the exact 
window sizes in KDE.

My current system is

GNU Emacs 21.2.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars) of 
2003-10-20 on zeus
Linux 2.4.something (distr. Red Hat 9.0)
KDE 3.1-10
gcc (GCC) 3.2.2 20030222 (Red Hat Linux 3.2.2-5)

No operands were given when Emacs was installed

I did not do any modifications into emacs. However, there are a few 
quite unusual specifications in .emacs: There are

=========

;;font size
(set-face-font 'default "7x14")

;;my favorite scrolling and margins
(setq scroll-conservatively 100)
(setq scroll-margin 4)

======

There are many different files where this bug occur. However, I attached 
one which definitely reproduce the bug at any time on my system.

You regret any guessing from my side. However, I guess, that the window 
size is very important. Thus, if I changed the window size this bug 
sometimes disappears and sometimes appears again. It occurs definitely 
if the window size is 611x632 px (which is default on my system for 
emacs) and mostly does not for the different window sizes. This 611x632 
size concerns  only to the attached files. For different files there are 
different "critical resolutions."
 
This bug is really terrible because it happens rather often and is very 
unexpected. I found it more than a year ago on my previous machine when 
I started emacs and found that it depends on my settings in .emacs 
file.  However, different setting are inconvenient for me. I hoped also 
it will be found and fixed by others. I thought it is because of my 
previous computer first. However, nothing changed when I changed the 
computer and installed latest versions.

Thanks in advance,

Anton Kulchitsky.