Just so everyone knows, this IS an issue with the Roku firmware.

The older boxes had this double code problem, the newest released boxes do NOT have this issue.
Also note: the firmware is not something you can update by clicking the software update button - that only updates the software.

I discovered this when I had an old Roku Ultra (when it 1st came out), one that I had gotten shortly after (for daughter), a customer's Roku Ultra (recently purchased), and a new Roku Ultra I just purchased the same time I got the customer's.
With all 4 boxes sitting on the desk, I powered them up and tested 1 at a time. The 2 older boxes had the repeat problem. The 2 newer boxes worked perfect with the same URC codes.

Good luck claiming a warranty issue with Roku however. I have been unsuccessful in getting them to swap the 2 older boxes with the repeat problem.