Horizontal tikz chain with labeled nodes is not aligned.

Question

The chain seems to be properly aligned without the labels; adding labels seems to break it:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
  \begin{tikzpicture}[start chain = going right, node distance=0, every node/.style={on chain,minimum width=10ex,draw}]
    \node [label=above:{a}] {1};
    \node [label=above:{b}] {2};
    \node [label=above:{c}] {3};
    \node [label=above:{d}] {4};
    \node {5};
    \node {6};
    \node {7};
    \node {8};
  \end{tikzpicture}
\end{document}

Answer 1

As mentioned by @percusse, labels are nodes as well, so the every node style applies to these as well. To align just "plain" nodes, define a new style.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
  \begin{tikzpicture}[start chain = going right, node distance=0, chain/.style={on chain,minimum width=10ex,draw}]
    \node [label=above:{a},chain] {1};
    \node [label=above:{b},chain] {2};
    \node [label=above:{c},chain] {3};
    \node [label=above:{d},chain] {4};
    \node [chain] {5};
    \node [chain] {6};
    \node [chain] {7};
    \node [chain] {8};
  \end{tikzpicture}
\end{document}