The alarm still works (which was my main concern), but it's an error nonetheless. I also noticed that when the icon is active, there's a message on the lock screen saying when the alarm is set to, but when it disappears the message on the lock screen stops appearing as well. Either way, I never had problems with the alarm not ringing at the right time.
I tried deleting the alarm and creating a new one, but the error remains.
Also, it began when my phone had Jelly Bean and now it remains after updating to Kit Kat. I have an I9505 unrooted with stock ROM.