Well, after fiddling with this start page mess for a few days, I better understand the behavior. I hate it, and it's not productive, but I hate it.
In a world where having many tabs open is a problem, Opera perpetuates the problem. There doesn't seem to be a way to go to the start page (speed dials) IN an open tab. One must click the + or the speed dial button in the sidebar (at the bottom left) which is both highly counterintuitive and requires you orient yourself from the address bar to find it.
Pinning the start page to the tab bar works the first time, but doesn't allow for opening the start page again in that tab.
I was an early adopter and moved away from IE, Chrome, Firefox and Edge. And this simple but profound change has me looking, once again, for a browser that is productive for me.