I know you all are looking into some instances of tasks with alarms invoking odd behavior.
Though I've run into the following problem on and off over the past month or 2, it wasn't until today that I could say with certainty that I've confirmed an instance of a wayward task alarm.
The task is Costco. It is originated on my desktop Outlook and sync'd to you using Gsyncit. The Task had initially been set for today, Tuesday. I changed the due date from Tuesday to Thursday either the end of last week or this past weekend. I'm not sure what iPhone calls it but my phone displayed your task alarm up through the blank timed out screen (I wasn't using the device).
I checked your website just now and the Costco task correctly shows Thursday.
There are 2 common denominators to similar instances of this problem. 1st, it only occurs on a task with an alarm that I've changed the due date. 2nd, the alarm always shows ~1 minute before. I always change the (in this instance) Costco dates in Outlook--Outlook does not have an ~1 minute, just you. Also, the alarm went off this p.m. and I always set the Outlook task alarm to the my preset default of 8 a.m.
Do you have alarms set to come from the device or the website? If you have alarms set to come from the device, then what probably happened is that you didn't sync your device after editing the task on the website, so the device didn't know the new due-date so it couldn't reschedule the alarm.
Tasks are edited either device or Outlook--never website. What u describe is possible but, IMHO, improbable--at least for my condition. The device was synced numerous times between time change and bad alarm. I'll come back if the problem reoccurs--