when playing nwn, seemingly at random the 3d part of the graphics will be replaced by a flat colour. often the compass goes black too. temporarily fixed by saving, exiting to main menu and re-loading the game.
as stated at http://nwn.bioware.com/forums/myviewtopic.html?topic=461888&forum=72 , the problem occurs when anything step-changes the system clock, such as ntpdate or ntpd correcting a drift too high to "slide".
solution: disable ntpd and/or ntpdate cron jobs, etc while playing nwn until a patch comes from upstream
I've added a note to the end of the ebuilds pointing to both this bug and the upstream forums. If an actual fix comes about for this, feel free to REOPEN it, otherwise there isn't anything that we can do about it.