Tower Armor in Twisted Treeline is Broken - Video Included

Towers in the Twisted Treeline appear to have somewhat broken values for armor. When minions are not around, turrets have 67,60, and 67 armor (going from outer turrets to nexus) however, when minions approach, these armor values go to -8, -15, -8 respectively. Here is a video I made that showcases what I am attempting to explain: https://www.youtube.com/watch?v=gWyJ7mMjjvs

Based on the armor values shown in game, the armor 'reduction' is applied correctly. When minions are close and turrets have negative armor, this is causing all damage done to the turret to be ~105% of the attack damage used. As a result, this causes minions and champions to be able to easily push towers quickly and with a bit of attack speed and attack damage, inhibitor turrets die in about 3-5 seconds. I'm not sure this is an intended mechanic, but it has made Twisted Treeline games be decided by one fight as long as the team that won the fight can push a wave into a tower. If this the intended mechanic, I'm sorry for wasting your time but would like to have some sort of response confirming that this is the case. Thank you.