Beware, one-time iOS alarms are not working right. Your alarm won't go off if you set it to repeat: never – e.g. the standard setting. However, if you set the alarm to repeat every Monday, Tuesday, etc, or just Saturday, it will go off.

The interesting thing is that this is the opposite of what happened after the clock change back in October. Then alarms set to go off on particular days of the week, e.g. Every Monday, Tuesday, Wednesday, Thursday, Friday, didn't go off.

We wondered if an extra second might have been added at midnight, causing this, but we checked an apparently no extra second was added last night.

According to numerous Twitter reports, which were then picked up by blogs including Engadget and TiPb, it is a problem with non-recurring alarms set from within the Clock application.

We were able to confirm this after a couple of false starts. For the bug to show itself, your iOS device must actually tick over from 11:59 p.m. on December 31, 2010 to 12:00 a.m. on January 1, 2011. 

Once you’ve passed that special minute and your iPhone has shot off its virtual confetti cannon, the bug occurs: one-time alarms set for 12:01 a.m., for example, won’t go off. (We were able to set a recurring event for every Saturday at 12:03 a.m., and that one went off.)

The workaround for this is easy: set your alarm for New Year’s Day to be an “every Saturday” alarm.

According to a 9to5mac report, this bug lasts through January 3, then fixes itself. We haven’t had a chance to test that claim.