Problem with Terrain

Hi guys.
Quite new to Unity (just started using it at uni), so still learning the ropes.

I’ve come across a problem with terrain/terrain tools. While trying to raise/lower the terrain using the tools, Unity seems to randomly lose track of where the mouse cursor is, and will think it is above where the cursor actually is on the screen. So while trying to create different levels in the terrain, it keeps switching between the two different locations, so it creates 2 of the same area next to each other.
Also, as soon as I let go of the mouse button, the lovely mountain ranges I have just created go extremely low res.

Is there anything I can do to sort this?
(If you would like a video of what is happening I can make one)

Thanks, StevieBruce

Well, I can answer the extremely low res question. The terrain automatically adjusts its level of detail based on distance. Try zooming in on your terrain after you’ve created it, and you should see it get more geometry detail.

If it doesn’t, it means that your terrain itself doesn’t have a high enough resolution. Check the documention for Terrain > Set Resolution… for more details about that.