FYI - I have the same problem in 4.9.  Even when I add a new page and try to delete the page I cannot.  Could it have to do with using the "display module on all pages" feature in the modules settings? I do have a couple text/html modules that I copy to all pages and it appears that it might give a clue to the problem.  When I added a new html/text module to a page and choose to put it at the top of my Left Pane the module is fine on the page I created it on, but, when I choose to display the module on all pages it copies it onto the bottom of the Left Pane.  I then tried to delete both modules in all instances and then create two new modules in the right order but when I add a new page the deleted modules are still appearing - so now I have four modules (I only had two pages on the portal).  So, either these are two unrelated problems or they are one issue that causes both problems.

 The issue on the provided states that emptying out the Recycle Bin should correct the problem.  For my case, the problem still exists even after the Recycle Bin has been emptied.