I tried to run your test script as a Junit plugin test and it worked fine without any errors. While I was investigating this playback issue, I found that, when you try to set a path to a folder in your system through WindowTester while recording say creating a new folder or selecting a file to open by browsing through that location in your system etc does not get recorded. Any dialog box opening, etc within the Eclipse IDE works fine and can be played back after recording.
I have a feeling that, this a bug with Window Tester. It fails to recognize the actions performed while recording related to system files/folders. What do you have to say about this? Or have I missed out some related package files while recording the tests.