I posted this in Bugs, also.
From the time I started using calculated shipping until just today, Regional Rate A boxes would be picked from my package preferences when that was the cheapest option for the client. However, today, it did not charge my client the Regional A price for a 2 lb package going to the further distance from me, but rather it picked the higher priced regular Priority Mail (Priority Mail box 1092) which ends up being a $2.00 difference. I have just checked all my listings that I measured my items specifically to fit into the Regional Rate A box if it was the least expensive option (I use size 12x10x2 as the item size) and now all those listings are not calculating for Regional Rate A pricing.
And while I know I can just use whatever box I want or refund the client for the overage however, this is the reason I chose to use CS so that I would not have to do refunds. Again, it has been working perfectly (including picking Regional Rate A boxes) until today. Hoping my CS gurus here might have an explanation!
:-)