I’ve used the multiple windows, it does take some getting used to.
I’m experiencing something different, where a dozen open tabs will disappear. I’m suspecting that they get killed when you click a link in mail and it opens safari, but not every time. Then when you go back to safari they’re all gone. Weird.
I’ve seen that. . . clicking a link in Mail will often open a new untabbed Safari Window. Other times it adds the link to your currently open Safari window. It depends on the script being used. Your original fully tab populated Safari window is still present, it just doesn’t have current focus. It took me a while to catch on to what was going on. I’m not liking that new feature; it feels more like a ‘bug’ to me, but I understand why they chose to do it that way.