1. Yeah you are right. Somehow I never noticed it only happens for those buttons that don't display the full window name. Too used to them getting cut off I guess.
2. I searched again but can't seem to find this mentioned anywhere before. I know there was a thread about switchbar buttons (started by me) which explains a lot of the changes to switchbar behaviour implemented in 6.3, but it doesn't deal with this specific issue of highlight not being reset when mIRC is in focus again. Can you provide a link to the thread you're thinking of?