Debugging Craft plugin actions
I can confirm that Win8.1 + PHPStorm + xDebug and plugin code works fine.

Are you symlink'ing (using mklink in Windows) to your plugin code by chance? xDebug won't follow symlink's by default and at least in PHPStorm, you have to explicitly setup the path mapping in your project's settings to tell PHPStorm/xDebug where the actual paths to your symlink'ed files live.