hi to all - mouse problem

[caravel]

You say "they" move randomly? Is this one unit or two or more units? From what you've said here...

I click on the terrain and I hold left button and move my mouse.....
The unit move in another location (often just behind his actual location )and hold a single line formation (random vertical or horizontal).

...it appears that you're clicking and dragging, and this is causing the long think lines you're referring to. You need to click and click, not click and drag.

Edit: What is your first language? There may be someone here that can explain this to you.