Wiki article : https://en.wikipedia.org/wiki/Unicode_in_Microsoft_Windows#cite_note-10
This broke Firebird connection from all the Applications, our own and all third party Firebird tools we tested.
One of our customers had enabled that feature, and it seems to break lot of things. It might come as feature sooner or later, and definitely causes weird issue when enabled. And took lot of time to find the cause.
If this could be fixed before this becomes an huge problem (M$ decides to make this default option, they well could :D )