Default [Q] Verzion 900V probelm

I purchased a S5 G 900V (Verizon) on the 15th (of May) after my last phone died (Razr)... 2 months after the insurance expired of course. The S5 seemed to work fine for the first 3 days and like most I was setting it all up (w/exception of a few root only apps since the verzion phone is locked up).
This last Tuesday late afternoon the phone wouldn't turn on so I did a battery pull and when it booted up it had an unlocked icon (lock that was unlocked) display on the device and the word "custom" displayed under the open lock. The phone would go to sleep and not wake up without a battery pull each time. Device status under the settings area was also the word "custom". I had purchased the device from Best Buy along with insurance at our local mall... and at 7 pm after trying to get the phone to work correctly took it back to the store. The person that had sold me the phone was there along with one of the managers/assistant managers and they both keep telling me it was my own fault for attempting to root the phone (which I didn't do). They fought with the phone for and hour or so and couldn't get anything to work correctly... still getting the unlocked icon and custom word. I was told that if I could get it unrooted they would exchange the device for me, but they couldn't do anything with the phone until I could get it back into ua unrooted status. The assist manager did point me out to another website that explained the use of ODIN and where to get the stock Verizon rom.. which took a good few hours to d/l due to their slow server (not complaining, I'm glad they had it for me to begin with).
I set up and attempted to unroot the device with no avail. Did a factory wipe clean out cache etc etc the ODIN program kept saying it worked and I would be presented with all the normal new phone settings and hoops to jump thru as if it was just being activated... but on a restart the open lock and custom was still there.
Yesterday while looking over forums I noticed the phone was downloading an app I had already downloaded. I looked at the phone and it seemed as if it was re-installing some of the basic play store apps I had! I rebooted the phone and no lock appeared and under the Device status custom was gone and "original" was in it's place. I packed all my boxes and cables up and after work today took the phone in and had them exchange it for a new one. The same assistant manager was there when I had first taken the phone in when I had experienced the strange behavior.
She (the assistant manager), had no problem exchanging it since it didn't have that error showing up.
My major concern is if somehow if/when I connected the phone to my desktop did it (either the phone or computer) try and transfer files that made the phone act up in the first place? I have a rooted Nexus 7 and the Razr I had had ... had also been rooted. I don't think I have anything besides Samsungs device manager and Wugs Nexus Root toolkit, but those shouldn't mess the S5 up I have Eclipse installed but it doesn't launch without manual opening. I would both hate it if I had the same thing happen to this new phone but also dislike the idea of not plugging the phone in to transfer media if I wanted to.
Any ideas... or think it was a bad first phone?