main=422,1079,266,725,3,0,0
I see the 3 means minimized. Maybe this has always been the behavior and I never noticed until now because of the tooltip. It's the tooltip which really annoys me though, so if this starting minimized after rebooting is intended (seems strange) then okay. But I'm confident this tooltip has not been appearing the whole time.
Or is mIRC.ini failing to save every time I reboot? Is that why I have all these 0B mirc3928470.tm_ files? I have turned off all remotes for testing in case some hanging dll may have been the cause. This time I noted the timestamps - mIRC.ini was stamped 9:41 when I rebooted Windows. After logging back in and before starting mIRC, mIRC.ini is still 9:41 and there is a new 0B mirc7197848.tm_ stamped at 9:44 which is the time I rebooted.
So it seems these are 2 separate bugs, I have probably been experiencing this failure-to-save on reboot for a while given the tm files. Then the tooltip appearing is the new bug which I think coincides with the new Windows build.
And note: the tooltip pops up even without having to restarting windows. Just close mIRC while it's minimized and when next you open it, it will start minimized and the tooltip appears.