Hmmm... I just noticed this: under "File", command-T is "New Tab", and under "History" it's "Reopen Last Closed Tab" (which command-Z used to do).
Can't help with your Safari troubles but in case you're not aware, command-z is Undo.
My mistake in saying "used to do"; it still does.
Command-Z, "Undo Close Tab", is the command I've used
for that purpose since time immemorial; as far as I can see it serves the same purpose that the command under History serves when/if it works correctly, and it's easier to reach on my keyboard. And to be perfectly honest, I forgot all about the keyboard command to reopen a closed window a looong time ago and do it - in a very cumbersome manner - from MenuPop > History.
