transform breaks when building on windows

[liady]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When building with Webpack on windows, each css fails with
Module not found: Error: Cannot resolve module 'C:folderNamesrccssVariablesPolyfill'
(the path to the transform module, stripped from slashes)
The tests also fail on Windows.

If the current behavior is a bug, please provide the steps to reproduce.
Run tests on Windows, or a Webpack config with a tranform module for style-loader.

What is the expected behavior?
It should not fail when building on Windows.

Please mention other relevant information such as your webpack version, Node.js version and Operating System.
Webpack 1.14.1
Node 5.0.0
Windows 10