This has reappeared in 7.68, mIRC is running on Windows 11 which I am connected to via remote desktop. I had installed a few of the earlier betas, I did not notice it then. I might not have installed the latest beta(s).
I could not reproduce via steps in this post https://forums.mirc.com/ubbthreads.php/topics/269905/duplicate-icons-bug#Post269905
so I don't know what the cause is