I have no problem drawing precise lines that do not snap to the magnets of shapes.
Just choose a clear part of your canvas that does not have many shapes in it. Auto-attraction of lines (at least on my OGP 4) is only within 0.4cm.
Draw, holding ⇧ down, if you want straight lines on the cardinal axes or diagonals. Get the exact length you want either using the ruler (watch the dotted lines move on the ruler) or the Inspector/Properties/Geometry.
Pick the line up and move it where you want (eg. where there may be many shapes that would invite a snap).
You can lock a line or shape, so that further changes are prevented.
In the Inspector/Properties/Magnets, You can also turn off all magnets or remove specific magnets from shapes, useful for shapes that you do not want lines auto-snapping to them.