“No, no, no, no, no. You said you’ve got line of fire here.”
It doesn’t “cheat” you (as this implies intention), it just has bugs. If this is your playthrough, I’m sure the devs would love if you could post a savegame with this where they could see it and fix it.
I’ve encountered this bug a couple times as well.
Intended or not, it said - “Yeah you have 100% hit chance from here” - then, when you actually moved there, it goes - “Nope. You don’t have the line of sight.”