Authorize.net API - credit card order converts to check/money order

Hi All

Zen 1.2.7d

Two payment options: Credit card (Auth.net AIM) and Check/MO

A number of customers have stated that they have selected the credit card option (displayed above check/money order), entered their data, submitted, but then the cart comes back saying that their order is a check/money order payment.

This has happened a number of times for quite a while.

1. Has this happened to others?

2. What might be the issue?

This was just reported again by a customer that we believe knows what they are doing.

What do you think?

Many thanks