Hi,
You don’t have to uninstall the W3 Total Cache to solve your problem.
First try to put “/wp-content/plugins/woocommerce/assets/css/woocommerce-smallscreen.css” without the quotes in the textarea for the “Never minify the following CSS files:” on the Minify setting page, and then empty the Page and Minify Cache. This solution apparently is working for some installations!
I have this problem on another theme I bought but, the solution above is only working for my theme developer. In my case, W3TC loads a minified CSS file after the custom inline CSS generated by the theme.
I am still searching for a solution!
WordPress version 4.1.2 and the latest versions for all the plugins.