I just did what you describe in Netscape 4.7 on my Linux box. No multiples.

I have noticed that if you hit the 'comment on' link, the first form that pops up actually creates the writeup. If you return to that first screen and hit the submit button again, it will create another. (There's a hidden field named op set to new for only that page.) On all pages generated after that first submit, not only do they use POST instead of GET, but there's no op set.

If you hit submit multiple times, it'll presumably do the same -- I don't think the 'duplicate node creation' thing is fixed in the latest tarball.