That's what I first thought as well, but it doesn't make sense?
Let's say you set an event notification for "100 seconds from now". Let's say 'now' is 0s, so that you get the event at exactly 100s.
Now a time change comes along at 50s, which sets the clock back 50s.
So when the clock ticks through 100s for the event notification to occur, the clock ticks through to 50s, time change makes that 0s, then the clock again ticks through to 50s, triggering the event, and the clock ticks merrily onward from there.
The event thus comes at the new 50s, not at the new 100s.
I.e. the alarm goes off -before- it should have gone off. The bug as stated in the story, however, has the alarm going off -after-.. essentially at 150s. I think.
So if an alarm is set for "7 hours from now", and the clock ticks go like this:
0h, 1h, 2h, 3h/2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h.
And the alarm says "in 7 hours I should go off", rather than "at 7am I should go off", it would look like this:
0h, 1h, 2h, 3h/3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h.
Thus making the alarm go off at 6am - not the 8am in the story.
Did I mention I'm confused?
( I do hate DST as well, for this very reason, but I still can't fathom the bug. )