I've also noticed when 16 is open and I can see lots of the pages, right at the bottom is one page which has got three areas of cms on it (the only page with multiple input areas). This is the only page closed and if I click on it for a second you can see the content scrolling under it but it won't open.
But I can see those pages in view/edit.
So I totally deleted the three content pages and rebuilt from scratch.
Its still the same and I reloaded the html web page as well.
Any ideas please.