Cutting into a shape

The other day, this worked perfectly fine, but today it doesn't: I wanted to cut a piece from this line by selecting a square where i wanted to cut with the rectangular tool, then selecting both the rectangle and the shape i wanted to cut, divide, done. Like i said, this worked perfect before, but now all i get is this

Also tried it with the linear tool, got the same kind of thing happening

All i want is just an open space in between that shape