Sorry, took me awhile to understand the post -- I am getting old I guess

So if I understand corretly you are just wanting to add "New Post" link to the "div class=navlinks" on showthread template.
My initial thinking is that you were running into a DOM situation, so I decided to try it myself. Unfortunately, I did not have any problems, but be very careful about html comments in this area. Post the code you are inserting and I will take a look.
Or maybe I have the whole question wrong?