Earlier quoted context omitted.
They're just as bad at identifying actual "weapons": I flew to South America with a layover in Miami a few years back. Got past TSA without any trouble on the domestic leg, then I had to go through again for the international leg. The second time through security, they said they saw a blade on the x-ray.. turns out they were right. I forgot I had left a multi-tool in my bag. Thankfully, they just trashed it and let m…
Very similar story about MIA. I flew out of ATL with a pocket knife, and lost it at MIA on the way back. Also conversely, ATL wouldn't let me carry-on my pool cue and forced me to check it, but at YUL on the way back, they had no problem with it. I think it's more of a roulette of circumstances more than a pattern of compliance/negligence, but it is curious to have 2 MIA data points.
I also flew Oslo->Lisbon->Sao Paolo->Rio de Janeiro->Lisbon->Oslo about five years ago with a 7" soldering iron in my hand luggage.
Then there was the time when I had my bag very thoroughly searched flying out of Geneva because of a highly suspicious loaf of bread.