Okay, further testing yields some interesting results. I think everyone should know this, because I feel it is an important difference between the AT&T firmware and the non-branded firmware.
After doing a full flash of the AT&T firmware, I was able to get the reset protection with GDR2 and Denim. However, the difference between the "unbranded" firmware and the AT&T branded firmware is enough to make me want to go back to unbranded.
Here's why:
1. AT&T branded version of GDR2 takes a full 40 seconds longer to do a soft reset.
2. AT&T branded version of GDR2 downloads on the LTE bands approximately 30% slower than the country variant. ?!? Why? I don't know.
3. I have to perform a soft reset using AT&T's version every time I try to do Internet Sharing, otherwise, I am unable to connect, even though it shows successfully shared. I can only connect after a soft reset. I don't have this issue with the country variant ROM. The country variant ROM allows me to connect every single time and never has an issue.
4. App switching is noticeably slower on the AT&T version, though only slightly. "Resuming" when back to the start screen happens much more often, and I don't mean only slightly for that one.
5. If I have internet sharing on, or if I'm using the phone's Wi-Fi, and then I get a call, the AT&T version will cut off my Bluetooth at the time the call comes in. I have to perform a soft reset to get the Bluetooth working again. This does not happen with the Country Variant ROM.
There are other reasons as well, such as all the garbage apps that get installed with AT&T, and the country variant is "clean" installed. Easy enough to uninstall all the apps, but apparently there is still other garbage there that affects the performance of the phone.
This probably is not a complete list. Just the things I noticed when switching between the 2 ROMs on the same phone. I think for any phone I get from now on, I plan to flash it with an unlocked country variant straight away. No wonder AT&T takes so long to release updates. They have to tinker and mess things up first. With the number of problems I have found after using the Country Variant for a week and AT&T ROM for 24 hours, it concerns me how many other things are wrong with this AT&T update.
Just my 2 cents. Perhaps other people aren't having the same issues. I'd say the "speed" issues are the biggest for me at this point, as it deals with everything I do with the phone. Makes it more sluggish by 10-15% I'd say.