Bug 1: I was unable to reproduce this. None of the mIRC window titlebars are shown as active and the highlighting is correct. If you place mirc.exe and an empty mirc.ini in an empty folder and test from there, does it still happen? Changing any settings, or even maximizing windows, can make a difference to the result.
Bug 2: All focus-related features/scripts in mIRC are directly dependent on Windows focus messages, so the reason for this behaviour is that Windows has not sent any focus messages to mIRC since it is not the active application. Focus messages are the only reliable method of determining whether a button should be pressed. For example, it is possible for a window below the top window to have the focus, so window position in the display order is not a valid method of determing whether a button should be pressed or not. Windows can open minimized, behind other windows, on the desktop, and so on. Changing the switchbar button display to work independently of focus events would result in the switchbar not being synchronized with focus messages, such as highlighting, scripts, and other focus events.
