EDIT: Updated the post
"No paint the last pixel" confirmed in "Winterleaf" version. This bug is also preset in the "signmotion" version.
the error is present at the "bottom/top" of my terrain.
Is necessary to paint the top to paint the "last pixel" of the bottom.
If you don't paint the top...
If you paint the top, the bottom is painted.
Any terrain tool only work for one terrain at the time, what the cursor is pointing. So you need to raise one first.