Force line break in tabu "X" environment

Question

I would like to force a new line within a tabu 'X' column. Using \newline forces a new line, but includes some ghost spacing, making the text no longer centered.

I have tried using \\ in combination with both minipage and makebox without success -- both give errors and do not compile.

\documentclass{article}
\usepackage{tabu}

\begin{document}
\SweaveOpts{concordance=TRUE}

\begin{table}
\begin{tabu} to 4in{|X[1,c,m]|X[3,c,m]|}
\hline
Column 1 & Column 2 \\
Some text & Three lines \newline of text \newline here \\
\hline
\end{tabu}
\end{table}

\end{document}