Knitr problem

I got some weird problem with my R workflow recently. For example, the very simple code chunk below:
--------------------------------------------------
\documentclass[preview]{standalone}

\begin{document}

\begin{figure}
<dev='tikz'>>=
library(ggplot2)
qplot(displ, hwy, data = mpg, colour = factor(cyl))
@
\end{figure}

\end{document}
--------------------------------------------------
would not build correctly. Sometimes it gave error message, sometimes it created empty page, etc. Installing the latest version of knitr from the github repo seemed to solve the problem.