Address bar, yes :-D
I copied the URL from the address bar of another tab. When pasting it to a new tab, it pasted something else. An URL I had either copied or visited some time earlier. (I tried both cmd-c / cmd-v and right mouse button context menu copy & paste.) Using "Paste and Go" pasted the correct URL in the clipboard. (Restart or reboot didn't help.)
However, I just checked, and today's update (0.99.123.2-beta) also fixed this in addition to the new tab issue. If you weren't aware of either issue and they were just accidentally fixed, then… I guess that's kinda weird and I wonder what the problem was… Perhaps my configuration was somehow corrupted or something like that and the new version just overwrote it?
But, both problems solved in any case, so all good :-) Thank you!