Distorted line in mesh [Object Mode] I have done some sculpting on the mesh (things looked all right) then when I switched to Object mode, I saw some weird lines pointing out from the mesh.

What is causing these (as I see them often) and what are the solutions for these?
There are duplicate vertices where these lines appear. For Multiresolution this is a problem. Afaik you will have to correct these spots by hand after removing the doubles.
You can see them more clearly in Editmode after pressing Apply Base.