I have a 3 monitor setup, where the middle monitor is the main monitor. I like to have mIrc on the left monitor; however, every time it is restarted, it comes up on the main monitor, in the same position as on the left. Pretty annoying, as it has to be moved every time.
At a guess, the negative x coordinate for the window position on the left monitor is being "fixed" somewhere, without checking that the monitor is actually there. I'm pretty sure it used to work some versions ago (can't point out exactly when it broke, sorry). Am running the latest public release.