This one is pretty big in terms of consequences I think.
For a few month, I've been thinking I was getting too old for this job. My code was sometimes doing the opposite of what I wanted, and my customers data even got meaningless sometimes.
It's true (or false, I'm not sure anymore) that in pure logic, A and not A are quite different things.
But with FileMaker 16 on Windows, here's what happens (see video attached and pay attention to the 'not')
Thanks to lem_alpha who could reproduce the bug and reassure me.