I'm having the exact same problem with my SECOND SCH-u740. It's really obnoxious. The alarm will go off, and then I'll go into my calendar to delete the entry, and the entry is nowhere to be found.

My first phone did this, and I took it back. Verizon swore up and down that they couldn't find anything wrong with the phone. Then it did it again, right there in front of them, so they gave me a new phone.

Now it's doing it again (and it will continue to do it, once every hour, at (9:15am, 10:15am, 11:15am, 12:15pm, etc. etc. etc.).

I plan to take it back today and get ANOTHER new phone. I'm truly very aggravated.