Mouse Jumping Issues In World Editor

I am currently creating a map in world editor but when I use the "Raise Height" tool in Terrain Editor the mouse will flicker back to the exact same spot on the map several times a second. This creates a large bump in the land as the flickers raise the height of the ground each time, and the ground becomes patchy and uneven when I am trying to raise the land on other parts of the map.
Does anybody know how to fix this issue, or have any idea what could be happening?
Cheers.

 

Yep it is, Thanks for the help!