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It's neither a bug nor a feature of Remote Buddy.
It's a feature of Mac OS X Quartz Display Services, though. The 
display fading automatically will be terminated if it is not 
programatically terminated within 15 seconds:
http://developer.apple.com/documentation/GraphicsImaging/Reference/Quartz_Services_Ref/Reference/reference.html#/ 
/apple_ref/c/func/CGReleaseDisplayFadeReservation
Quote:
 Fade reservations are valid for up to 15 seconds.
  That also means you can't fade a display for longer than 15 seconds 
(limitation enforced by the interval {0, 
kCGMaxDisplayReservationInterval}, whereby 
kCGMaxDisplayReservationInterval is 15).
Best regards, 
Felix Schwarz