Probably due to misleading/contradicting specifications by hardware vendor.
Mya be inspected on 'americium.suse.de' (ia64, but behaves as bad on ppc).

Reprint of "Specification" from "Quick Setup Guide":
 Input signal format
   RGB operating frequency*
   Horizontal x Vertical:
     28-92 kHz x 48-85 Hz (analog RGB)
     28-75 kHz x 60 Hz (digital RGB)

 Resolution
   Horizontal x Vertical:
     Max. 1920 dots x 1200 lines
     1600-1920 dots x 1200 lines
     (Only when the vertical frequency is set to 60 Hz.)
[...]
 * Recommended horizontal and vertical timing condition
   o Horizontal sync width duty should be more than 4.8% of total
     horizontal time or 0.8 us, whichever is larger.
   o Horizontal blanking width should be more than 2.5 usec.
   o Vertical blanking width should be more than 450 usec.