Sorry for the long post, I just want to provide as much info as possible...

After a long conversation with a CSR last night, I was still left confused about the 2 degrees billing cycle, and was wondering if others had
a) experienced it
b) could explain it

I am on a post paid plan with 120 minutes + 100 bonus minutes.
I am on a billing cycle of 17th - 16th of the month.
Yesterday I receive my bill, and saw call charges for national calls (ie those covered by my plan minutes).
I checked the 'My usage' section of the website for the latest billing period, and for the 16th Jan (the end of my cycle) saw that all calls were still $0.00
Hmm, so my usage is showing calls still zero rated, but the bill shows them as being charged.
OK, I selected the latest billing cycle and "downloaded transactions' to check it more thoroughly in Excel.
Loaded the file in Excel, and it shows all calls for the 17th Dec - 16th Jan as $0.00
Weird.
After a long conversation with the CSR, it appears that the charges relate to calls made on the 16th December (the previous billing period).
Check my previous bill, no call charges.
Check the downloaded transaction file again - it only shows 17th Dec - 16th Jan.
Check the 'My usage' webpage again, and go to the last page - it shows the 16th December, and indeed the calls charges appear!
OK, we can now see the calls the charges relate to.

But, (and here's where the CSR couldn't explain it) why are call charges showing for the period before my cycle. They're not on-charged, these are calls made form the 2 degrees network. I thought my cycle started at midnight on the 17th (indeed the 'download transactions', and the plan minutes agrees with me), but it seems as though the bill creation starts 'at some point' on the day prior'.

So, the question is
a) am I weird in thinking this
b) does it seem strange to others
c) is there an issue with their billing system

Thanks