i found a bug right now when changing something on the address book..
1. run mirc
3. /join #anychannel
4. press alt+b/alt+k, click on the about button or open any other dialog
5. press alt+2 to change focus to '#anychannel' and it won't work correctly. the channel will be displayed but the switchbar button will still look as if the channel was not the active window.
i've tested it several times and got the same result everytime.