Terrain Height Tool Glitch

While in the World Editor, when I use the Terrain Height Tool everything goes fine until a certain point.
When I reach that certain height the terrain just resets all the way back to the bottom, and I can't seem to find any way to fix it.
Can someone explain this please? Is there a limited height?
Thank you!

 

Nevermind, I just had to up the MaxTerrainHeight, but unfortunetly another problem occured. Turning up the height and then using the FlattenTerrain (own height) to flatten it, after doing so the texture of the ground is just clear, nothing...
Please, how do I make the texture go back again.
Thank you!