OK, I see why that was and I believe I've fixed it now - I even logged in as you and checked, and it's showing the link in the navigation popup
Yeah, that's it. 76 was uploaded two minutes later than 77, and the API returns stuff in publication order. On the website, they appear in the order you (@aran) linked to them when you edited the page, but the app will show them in order of upload time.
I could of course change that to be alphabetical, but bear in mind that perhaps there are other places where publication order rather than alphabetical is what you want, and it could break the ordering of those. (I'm unsure if that's the case, but I wouldn't want to alter the ordering without having checked.)
So instead, I've just manually fiddled the upload time of number 77 by a few minutes so that they order correctly