Strange "boldification" of letters

[Torsten Bronger]

Hallöchen!

I observe the following effect with my Emacs 23.0.60.4 on a Gnome
desktop: http://www-users.rwth-aachen.de/Torsten.Bronger/emacs.png

As you can see, the letters "i" and "r" to the left of the cursor
(and the preceding line) are much bolder than the others.  I
achieved this by pressing "up arrow" and "down arrow" many many
times, alternating point between the "n" and the "o" (so, the
right-hand-side neighbours of the bold letters).  By doing this, the
letters became gradually bolder.  The typeface is "monospace-14",
the cursor is non-blinking.  As you can see, sub-pixel anti-aliasing
is switched on with Gnome.

Only some letters are affected.  i, r, x, s, k, w, as far as I can
see.  But "m", for example, stays thin.

What's going on here?

Tschö,
Torsten.

-- 
Torsten Bronger, aquisgrana, europa vetus
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