An indentation problem with TikZ nodes and foreign document classes (babel)

Question

I'm new to LaTeX and i'm struggling with TikZ, especially flowcharts. I'm dutch and therefor I'm using the documentclass 'rapport1':

\documentclass[11pt]{rapport1}  
\usepackage[dutch]{babel}

This documentclass has a default parindent which I managed to erase with the following line:

\setlength{\parindent}{0pt}

This line however seems not to affect the indentation within tikz nodes:

\documentclass[11pt]{rapport1}  
\usepackage[dutch]{babel}

\setlength{\parindent}{0pt}

\usepackage{tikz}
\usetikzlibrary{shapes, arrows}
\tikzstyle{block} = [rectangle, draw, fill=blue!20, text width=5em,
                     text centered, rounded corners, minimum height=4em] 

\begin{document}
    \begin{tikzpicture}[node distance = 2cm, auto]
        \node [block] (test) {This is a test!};
    \end{tikzpicture}
\end{document}

Is there a way to solve this issue and get the node block rendered just as it would when using \documentclass{article}?

Answer 1

Just set \unitindent to 0 pt instead of changing \parindent:

\setlength{\unitindent}{0pt}

This is used by the class, in rapport1.cls we find

\newdimen\unitindent
...
\setlength\parindent{\unitindent}

Specifically, \parindent can be reset to \unitindent by internal class macros, such as \@indentset:

\newcommand*\@indentset{%
            \global\parindent=\unitindent
            \global\leftmargini=\unitindent
            \global\@needwriteindenttrue}