# siunitx with product-units, scientific-notation and exponent-to-prefix

When using the siunitx package I have noticed some strange and unwanted behaviour. I was hoping someone can help me determine if this is a bug or I'm just using it incorrectly.

I've created two cases:

\documentclass{article}
\usepackage{siunitx}

\begin{document}

Case one: \SI{0.9x3.5}{\mm}

Case two: \SI[scientific-notation = engineering, exponent-to-prefix]{0.9x3.5}{\mm}

\end{document}


which gives the following output:

Clearly, Case two is incorrect. I would expect either 0.9mm x 3.5mm or 900um x 3500um, preferably the former.

I've used the options in Case two as part of the siunitx package options for my document, and the incorrect behaviour occurs throughout my document. I know it is possible, but I'd rather not manually unassert the options for each case where this occurs for the sake of code flexibility.

I'd really appreciate any help or suggestions. Thanks in advance!