I bet I'm not the only person to notice this issue...
To recreate the issue:
I receive a text message. I touch the icon on the lock screen and slide it down to unlock it, then go to my Messages app. I'm using the Messages (not Messages+), BTW. I go to the contact that sent the message and view / reply. I then hit the home button at the bottom of the phone.
That contact replies, so the lock screen starts to flash. I touch the icon and slide it down. I go to the messages app, and the original contact opens automatically. I reply, and then hit the home button.
This goes on for several messages.
At some point (say 10 messages later), I decide to send a message to another contact, so I hit the back button on the phone. It takes me back to the main conversation list, then hit back again and it takes me back to the original contact I was messaging previously. I hit back again and see the contact list, then hit back and it takes me back to the original contact. It will do this for each of the times that I went straight to the contact using the "To recreate the issue" section above.
I believe there is an issue with the phone not handling application status properly. The 'back button stack' isn't being managed like it should, so I can end up in what appears to be a loop, until I hit the back button enough times to actually back my way to the home screen. This isn't how it should work, based on documentation I've seen and read from Google and various Android development books.
I am running:
System version: 21.44.12.quark_verizon.verizon.en.US
As I said, running the stock Android / Moto Messaging application (NOT Messaging+).
That isn't the newest version of the OS. The Android 5.1 update has been available for a couple of weeks now. Perhaps the bug you found was fixed in the update.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.