Yeah, I've seen it myself with our backups in the past. I think what causes it is when you have backups which start/finish near to the time change, and it gets confused. I think Backup Exec must use a relative time or something, so if a backup starts at say 9pm, and finishes at 11pm, it will get rescheduled for 9pm. However when the clocks go back this time will also get moved back, so it will now be scheduled at 8pm. Anything which runs after the clocks changed won't get moved, since their times are already set, and when they complete they will be scheduled correctly as the time has already changed.
Of course I could be wrong, and since it's a fair bit of effort to simulate, I only get to see it once or twice a year.