I used to find this annoying, but once I got over myself and my resistence to change I quickly started to find it extremely useful. Before, if I wasn't paying attention to the inactive mIRC window, I wouldn't know if someone said something in the active channel and would completely miss conversations due to not noticing a highlight... now I do. I don't think this behaviour is going back, so I suggest you do what I did: get over yourself, embrace change, and be happy.
I see how it can be useful if you only see the switchbar and not the active channel. I, on the other hand, see the active channel as well cause I have space enough (dual high-res monitors), so it's really too much for me in that regard. A simple tick button to turn this off would be something generous and profitable for everyone IMO, but I'm not a coder so I wouldn't know how much work it would be.
The button raise on active channel when mouse-over if mIRC is inactive is still looking like a bug to me, however.
