I’m certain this is not a bug, but designed to operate on “any key”
press allowing start/stop of a tune. I think the back key should be reserved for the browser behavior to allow a key to return to the song list (back in browser)
Huh, does Backspace normally go “back” in the browser for you? I remember that used to be the case, but all the major browsers (Chrome, Firefox, Safari, Edge) disabled that functionality because people were accidentally going back too often when filling out forms.
Eventually you will be able to customize the keyboard shortcuts to whatever you like. For now, these are the key bindings – you may know this but I’m repeating it for the benefit of anyone else who sees this:
- Spacebar starts/stops playback
- Enter starts/pauses playback
- Backspace restart section (one tap) or song (two taps)
- / go back to the song list and highlight the search field
That last one may be of particular interest to you, John! 
Btw for the web browser, Alt+Left on Windows or Cmd+[ on Mac (possibly also Cmd+Left) should go back to the previous page. These are the new standard shortcuts for navigating history.