I wanted to start a new thread for this issue reported by Chris
over on this thread with the hope that it will be easier to diagnose and get a fix going if it isn't comingled for the main topic of the other thread.
Chris's describes the error as "Just today, the customer sent out an email blast to their users and 10 out of 50 orders gave away shipping for free."
I had a client report this issue last week for the first time (SC 5.4.2 / DNN 6.2.6). They have 33 coupons, none of which offer or involve free shipping. There also aren't any shipping rules or anything like that - is uses very simple shipping options, no extravagant features other than the coupons mentioned.
Chris mentioned that "Addresses that are appearing on these orders are for the US and seem normal." The errant order I encountered was US as well.
Eric