On my dual-screen setup (primary 2560x1440 to the left, secondary 1920x1080 to the right) I keep mIRC maximized on the secondary; but after every mIRC boot (which coincides with a shutdown/reboot) it opens on the primary screen (still maximized though).
This sounds like a different issue. If you place mIRC on the second monitor and position/size it smaller so that it is in the center of the display and -then- maximize it, the "main" entry in mirc.ini will be the small position/size in the middle of the screen, so it will not be affected by being close to the desktop borders. The maximize setting is applied after mIRC is opened on the second monitor.
If you are still seeing this issue after sizing mIRC smaller, away from the desktop borders, this is a different multi-monitor issue.
Also, so that we can eliminate the multi-monitor complexity, can you test this on your primary monitor to see if it shows the same issue that the OP reported?
