Interesting Edi, as I have often read WD40 to be bad for blueing ? Certainly leaving your rifle wet overnight really not clever, but the degree to which this particular brand new T3x marked was quite amazing.
My mates T3x rusted badly after being put away damp. Overnight in a warm dry gunsafe, the barrel was badly marked. Truly way beyond what you would expect. No defending the fact it was not properly attended to after a wet outing, but the speed with which it reacted would suggest there is something lacking in their blueing.