I had the same problem. I used mIRC 6.12 or something, and my windows automatically updated my time to summertime today when I woke up and turned on my computer.
Well. mIRC starts automatically when I start windows, and I didn't bother looking at the clock, all I saw was the timestamp in mIRC - only when I visited some forums and one mentioned summertime I looked around and saw how my windows clock was 9 AM something, and my alarm clock was 8 AM something. When I looked at mIRC again, I saw the timestamp was 8 AM something so I was kinda freaked out
I tried to set the time in windows both forward and backwards, but little did it help. I tried closing mIRC and starting it again, but that didn't help either. I remembered recieving a network wide message thingy from Quakenet, that a new exploit was out, and that the current version 6.14 was vulnerable. So I thought to myself "hey, I DON'T have the newest version, having that might help me out here" - and as I updated (installing and choosing to keep my settings), the problem seemed to be fixed.
So I think a fix to this problem would be to install mIRC again on your current version. Just remember to keep your old settings, if you desire that..