Remote control issue with Amazon Prime app

I noticed an issue trying to use the Amazon Prime app on my XG1v4.

I normally use a universal remote. It's programmed with the XMP code set that Comcast uses for all their current boxes. It works fine everywhere, EXCEPT in the Prime app. For some reason, the OK key does not work, or at least not reliably (it will occasionally respond). Oddly, the XR15 remote works fine. An XR2 and a basic DTA remote also did NOT work in Prime, but work fine otherwise.

After unpairing the XR15, and verifying it sitll works in IR mode, I taught a remote the OK key code, and that did work. What is weird is that when I try to decode it to add to my main remote (my remotes are JP1 programmable), it would not work. Also, that 'learned' key will not work with the DTA in the bedroom, which should use the same code set.