It is explained in this link. It also tells you how to handle scheduled events that need to always run at a certain time.
This can be confusing but is expected. The scheduling of scheduled events is interval-based and not time-based. Notice that the original date of the scheduled event is still at your previous timezone (before the DST period changed), the scheduled event is simply repeating itself every 24 hour, which might mean that you will see a change in the local time it runs at, because during DST shifts a day may take 25 hours or 23 hours. This will cause a temporary shift for as long as the DST change lasts.