Qasar, this might be because of the projection you use to map your bitmap on the terrain. You should use "object standard" or "object parametric", so the mapping isn't dependent on the world coordinates, but on the object's own coordinates. Also check that the image map you use has a size of 1 in the material editor, both in X & Y directions. If this doesn't help, post a screenshot of your material editor, so we can see what's going on.