iPhone alarm clock bug leaves users of the UK has yet to return to work after the Xmas break, which is just as well for the portion that relies upon an iPhone for a morning wake-up.

For the second time in just a few months, a bug in the iPhone iOS software has meant that its Alarm Clock app failed to function properly, leaving many owners curled up in bed when they should be up and about.

The bug appeared to affect one-off alarms set for 1 and 2 January, but Apple reckoned that it would resolve itself by today — 3 January. Some users, however, are still reporting similar failed alarm problems this morning.

There’s no explanation yet for what caused the bug, but the 3 January ‘fix’ is thought to relate to the fact that the iPhone’s calendar doesn’t begin week 1 of 2011 until today. January 1 and 2 are still considered to be part of week 52 of 2010.

Fortunately, the bug only affects one-off alarms and not repeating ones. So, if tomorrow is your first day back at work, just be sure to set a new repeating alarm and you should be woken up as usual.

The alarm clock bug is the second to strike the iPhone in almost as many months. Last October, the alarm clock app failed to adjust the time of any set alarms to reflect the change from BST to GMT.