What the strange rule for replacing a ligature!

[Philipp]

What the strange rule for replacing a ligature! Where did it come from? I definitely didn't create it! How do I remove it?

[Erwin Denissen]

Normalization is a process that is executed by the shaping engine. I am not sure if all shaping engines do it, but it is common. FontCreator also works this way, to ensure you design and test your fonts the way it will likely behave in the real world.