The short answer (and with that I add the caveat that there may be an interesting longer answer) is that this behavior is intrinsic to the PerlMonks engine and would be highly non-trivial to change. Generally, any form containing the root post of the current page (given that it is such a page) will cause the post to be updated (but of course only if you have edit rights to that post). Off the top of my head, I don't know of any such forms other than the 'vote' form.

It is certainly worth documenting this behavior.