I wonder, of the people effected, how many of them thought it was a legitimate excuse for being late lol. (its not)
I've had little hiccups over the years with my cell phones and alarms on DST changes. On some models it doesn't immediately take effect until you actually open the phone and initiate some sort of communication, either by text or calling (Verizon). I've had LG, Motorola, and Samsung models over the years.
If being late is a serious problem, or issue for you, you should definitely have atleast 2 alarms. I would suggest 3, and do NOT place them all directly next to the bed. Atleast 1 alarm should require you to get up out of bed to disable.
This concludes my public service announcement (I was banned a few days ago for foul language hehehe).