V5 GMap?
 

Go to the very top of a gmap- and just keep heading right (or left) whilst at the very top and you'll just keep running in to a black screen o_O

Prime example
era_present_00-af.nw
Go to the top left of this level, head right towards the car tow place, and you'll run in to black, if you r/c it'll warp you back!
If you move down, it'll then load the level as it should, also if you check the x/y of the player it'll show as 63 for the y, when it should be 0! Does the same on NPulse

fix in v6?? cant test- not got it