I can't get compilation work by configuring the paths option for less-loader. And thus Less's preprocessing plugins (which may modify paths after they are installed) cannot work using less-loader.
For example, less-plugin-est injects some mixin code before compiling .less files and it also push its src directory into paths of the context. But after less-loader's WebpackFileManager taking over @import handling, Less stop searching paths for possible Less files.