A known issue... if you use Event Viewer, DST can cause unexpected behavior because Event Viewer changes the displayed time (and possibly the date) for events that have already occurred. For example, if an event occurred at 6:00 P.M. in standard time, after you move into DST, that event appears as if it had occurred at 7:00 P.M.

 

See...

(Note 031107: Also blogged at http://blogs.technet.com/dst2007/archive/2007/03/11/event-log-entries-during-the-2am-3am-dst-gap-why.aspx)