If screen resolution is changed with system-config-display (from 1024x768 to 800x600, say), and X restarted, the resolution isn't changed.
The reason for this, is that
/etc/X11/xorg.conf contains a 24bpp section only.
Section "Screen" Identifier "Screen0" Device "Videocard0" Monitor "Monitor0" DefaultDepth 24 ...
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