Revisiting the checkout review form multiple times creates a new order each time

This is the way it has always worked - it is not PayPal specific, so I don't know why you're citing #700270: Remove hook_uc_order('submit') as it is never called for redirected payment methods. Likewise, this has nothing at all to do with #644538: Duplicate order notification e-mail, and duplicate stock decrement.

There is a lot of discussion on ubercart.org about why it is done this way. I'm not going to rehash the discussion here. You may not like having those "In Checkout" orders, but it's not a bug.

I just upgraded to Ubercart 2.9 and suddenly I'm having the duplicate order issue. I have been able to recreate it, but for some the original order is "in checkout," but for other users, the orders are BOTH submitting . Because they have unique invoice#s/Order IDs... then Authorize.net accepts both of them as unique transactions.

The log is saying this:
22:38 - Delcined, #8715, Address is 1234 Steven's Rd., (AVS cannot match to cardholder to address) (this is the first order)
- it the browser's back button
22:40 - Approved, #1111, Address is PO1234, Lakeview Pl.
- changed address and resubmitted. Approved.
- Then for some unknown reason...
22:36 - Approved, #0342, Addres is 1234 Steven's Rd. (The incorrect address order is RESUBMITTED and approved this time).

Anyone have any clue as to why the old order would resubmit to Authorize.net and why it would be approved this time around?

@goliath173: I'm assuming this is the same as what you reported in #1608834: Duplicate Orders? If so, please add the information from #2 to that other issue. Regardless, it doesn't seem to have anything to do with this two year old closed issue.