The tabular option gives warnings in the log

[u-fischer]

This document

\documentclass{article}
\usepackage[default,tabular]{sourcesanspro}
\begin{document}
12345

11111
\end{document}

gives a number of warnings in the log

* fontspec warning: "icu-feature-not-exist-in-font"
* 
* OpenType feature 'Numbers=Monospaced, ' (tnum) not available for font
* 'SourceSansPro-Light' with script 'Latin' and language 'Default'.

tabular numbers are nevertheless used so this is only annoying.

The source of the problem is that the fonts don't contain a tnum feature, tabular numbers are simply the default. So sourcesanspro shouldn't use Numbers=Monospaced with this font:

\documentclass{article}
\usepackage{fontspec}
\setmainfont{SourceSansPro}%[Numbers=Monospaced] %gives warnings
\setsansfont{SourceSansPro}[Numbers=Proportional]
\begin{document}
12345 \par 11111

\sffamily
12345 \par 11111
\end{document}

[silkeh]

It took me a while, but this is now solved. Thanks for reporting!