Why does a path drawn from corner of a node doesn't align with the node path? It might even be non-horizontal while coordinates tell that it is. Who can I fix this?
\begin{tikzpicture}[thick]
\node (left) at (0cm, 0cm)
[draw, anchor=south west, minimum height=3cm, minimum width=1.1cm] {};
\node (right) at (3cm, 0cm)
[draw, anchor=south west, minimum height=3cm, minimum width=1.1cm] {};
\draw (left.north east) -- ++(0.8cm, 0cm)
.. controls +(0.5cm, -1cm) and +(-0.5cm, 1cm) .. ++(-0.4cm, -3cm)
-- (left.south east);
\draw (right.north west) -- ++(-0.3cm, 0cm)
.. controls +(0.5cm, -1cm) and +(-0.5cm, 1cm) .. ++ (-0.4cm, -3cm)
-- (right.south west);
\end{tikzpicture}
Sample:

outer sepfor a node is set to.5\pgflinewidth. This means that when you reference the rectangle node anchor the point is at the outside edge of the line when the node is drawn. To make the anchors reference the middle of the line useouter sep=0pt. – Mark Wibrow Jul 04 '13 at 11:03PGFandTikZdo not control this and merely insert relatively abstract path specifications. – Mark Wibrow Jul 04 '13 at 12:33outer ysep=+ptsuffices and makes sure that the\drawn lines only touch the rectangular border. By the way, they are rendered exactly the same way for SumatraPDF, Foxit Reader and Adobe Reader. – Qrrbrbirlbel Jul 04 '13 at 14:23