Did you get this dump from Listener? You can eventPlace an image or you can eventFill with a pattern. I don't see a way to repro the code you are showing. I could be missing something of course. Please let me know the steps you used to get the code above.
If you do not find a way to directly do it as you have tried (please post here if you do I am intersted), you may try this.I remember that we have used either text watermark, or something like open watermark file, copy, close file, paste, set transparency and mode, merge down, etc. Now we have settled with text watermark, (we use custom font).