Help Please - Flat shipping not working!

I am fairly desperate and was wondering if anyone else had the same problem.

I have 4 different flat rate shipping options and until recently it was working fine. Now it doesn't matter which option is chosen only the first option goes through onto the payment information page. When I delete all shipping options, even the first one, the first one still goes through onto the following page. Can anyone help??

Just to let you know that it doesn't do it all the time. It only seems to do it if I leave an item in my shopping cart, log off and log back on again, I think!

What version of Zen Cart?

Clean install or an upgrade?

If an upgrade, from what version and how did you do the upgrade?

You said you had 4 flat shipping modules ... what are their names?

Clean install - Version 1.3.0.1

Flat Shipping Modules:
flat - Australia Post Economy (NOT registered)
flat 4 - Australia Post Economy (REGISTERED)
flat 2 - Australia Post Express (NOT registered)
flat 3 - Australia Post Express Post Platinum (REGISTERED)

I had another customer complain last night that
"I got all the way to the end except the registered mail kept defaulting to a non-registered option so I tried a few things then bailed."

Please can you help as I am losing customers.