Can't close invisible tab

Safari 9.1 seems to maintain an invisible tab associated with a particular web page. When I cycle between tabs with ⇧⌘], it cycles through my visible tabs and then before cycling back to the first one, it displays a web page that I don't want. It's like I have that page open in an invisible tab. If I File > Close Tab, the page appears to close and I am taken to the next tab, but ⇧⌘] brings me back to that web page. If I Quit and relaunch Safari, it starts on my home page, but ⇧⌘] brings up this other page. There is never a tab shown for this page, but if I do View > Show All Tabs, the page is shown.

I've looked through Preferences in case this page's URL somehow got saved, but no joy. How do I get rid of it?

FWIW, the other page is on my local drive and is opened with the "file:" scheme. It is my local copy of a particular page of a remote web site I maintain. I edit the file locally and use Safari to verify the results before I FTP the page to the web site.