Yes, i have been hunting a bug for two weeks. Ok, i admit i procrastinated with side stuff like just to confirm that i am still able to write programs with syntactical meaning.
I am trying to stream in terrain tiles from my LOD algorithm (CDLOD after Strugar, height map extrusion), placing each tile where it belongs to in world coordinates. All went well, the selection algorithm put the bounding boxes of the selected nodes where they should be, the grid mesh used for rendering marched in correct order over the height map, and every other tile's heights were rendered correctly. Every other. Every not so other tile was just a huge flat (but correctly LOD'ed) grid. I spare you the pictures of a sad flat (but LOD'ed) landscape:-)
The error was that i had once switched texture lookups, like .zx instead of .xz for debug and to understand how lookups worked. I looked over that part at least 10 times, until it met my eye and waved to me.
Ok, ready to proceed to the next bug hunting :-)