The default date archive block is not showing the 12 months that I've specified for my Blog posts.

I'm currently running the latest c5 (5.6.1.2) after upgrading from 5.6.0.1.

This block seemed to be working when the site was originally at 5.5.2.1. however when I upgraded to 5.6.0.1. it seemed to stop working. And now today (June 28th, 2013) I just did a test on my local copy of the site and upgraded from 5.6.0.1 to the latest version of c5 (5.6.1.2) and the problem is still there.

WHAT I'VE TRIED:
- I have cleared my c5 cache and the browser's cache
- disabled cache within c5
- uninstalled and reinstalled the date archive block
- Tried applying a core theme to see if there's any difference
- Turned on c5 debugging (no errors are displayed)

SOMETHING REALLY STRANGE
- I changed my computer's date back to May 2013 (the month before the update to the latest C5) and I get my previous 12 months that I specified... HOWEVER, I'm now missing my June and July 2013 months.

UPDATE:
Now that it is July, the date archive shows June and July... June because this is when I upgraded to the latest c5. It however does not show my May post or anything before June.

Is anyone able to shed some light on why this is happening?

Thank you.

- Michael -