pro kerry are ya there wacko. Now getting back on topic, im not sure if this will help but did you put any settings on the compiler to make it run faster? like -fast? Thats happens to mee somethime when im on a really low texture setting in the game. Try making the brush bigger or using a different texture, because i think it has to do with "oway out of proportion" textures
It's a bug that happens very often, when creating a brush like 100 x 20 x 100 units, and give it a texture, and you extend the brush on one side to for example 400 x 20 x 100, the game won't draw the texture that should be there (the new piece you extended), only the color pixels that touched the one side of the brush (100 x 100), that's why you see those lines, in the editor you won't see this. But it is very rare.
Happens me 2 times once with grass textures.
Just re-texture, or rebuild it.
It also happened me once with LOD terrein, but that was because I messed a lot with the scale, so I couldn't see the hole texture in the game, except in the editor.
same thing happen to my grass brush i had to re-texture it was really weird. coz when my map was played and the next map in rotation was st renan the st renan map would get the wierd texture problem.