xf86config.py:453 sets the monitor name to "Generic Monitor" if it can't detect the monitor using DDC. This causes two monitor sections with the same name to be generated, and the settings set in kickstart go into the second section. X pays attention to the first one. They need different names. Workaround: run Xconfigurator --kickstart in %post section.
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verified this is still a problem in 6.2 ...
*** Bug 11701 has been marked as a duplicate of this bug. ***
fixed for next release