I'm not sure if this can be considered a bug or just a change in how it works that will require some scripts to change. But here goes...
In pre-beta versions of mIRC, if you right click a nick in the channel, it will highlight the nick in the nicklist. In beta 7.23, it no longer highlights the nick in the nicklist.
Now here is where I see it causing a problem. Note that it is really not that big of a problem and can be changed in the script to work, but I'm mentioning it anyhow. Let's say you have an alias to voice nicks, which can voice any number of selected nicks. You want to call that alias from both the nicklist popup and the channel popup. You can do this in a few ways, but for this example, let's say that you're just calling the alias. You want the alias to verify that a nick is selected, so you check $snicks($chan,0) or $snicks($chan,1)... the first giving 0 if nothing is selected, the second giving $null if nothing is selected. In pre-beta, this works. In beta, it does not because the right click doesn't select a nick and if you've never selected a nick in that channel, no nicks are selected.
Now, let me be clear that there are other (better) ways to deal with that situation, so you don't need to point those out. This just came up and I wanted to report it because there may be other situations where it might be necessary to highlight the nick that was right-clicked that I'm not thinking of. If it appears that this isn't going to have any major effects on scripts, then don't worry about it. But if it looks like it might cause problems, then it might be good to make it work like previous versions of mIRC.