Just seems strange
same cylinder same symptoms and just wondered if this was not a rare thing

 

While your exact situation might not be common, problems with spark plugs being stuck or stubborn are common on these engines, and just about any engine where a spark plug stays in for 100K miles. All the heat cycles, crud down in the spark plug hole, etc... all make for a fun job sometimes. Maybe a previous owner had a problem and boogered the hole up, and youre now dealing with it. I've worked on quite a few of these, and never come across the same problem youre having. But with 10 million of these engines, there are bound to be a few odd things happen. Hopefully you can get it figured out. I would take the head to a machine shop and see if they can drill out the spark plug hole, and press an insert in for you.

 

A good machine shop will be able to correct that thread problem.
Seems like someone used either an air driven tool to remove or install a plug , or over torqued the plug at one rim or another. The plugs only take 15 ft/lbs torque.