Yes, this is the way all links work and bookmarks as well. Note that PDF is not the only format with multilevel links in the TOC. Certainly true of ePUB as well and probably mobi. Currently the top entry on a page of multilevel links goes back to the previous level which is also what the exit (back arrow) key does as well. I see no need for the two methods and have proposed that the first entry actually go to the entry in the eBook. Currently, if you have several levels in the TOC only the most detailed entry will actually go to the ebook which means if there is text between the levels you can't directly reach it and more keystrokes are required.