You are right, Quantumbro's Death role reveal specifically said that he could not target himself, yet on night 4 in his reveal post he says that he switched amir0x and himself.
Night 5 he said he switched Karkador and Traube
Night 6 he said he switched Absolutbro and Robotninjahornets
then again before he died he said that he could switch others with himself
I think he threw that in so that Mafia would think that he could switch himself, because to do anything else would have instantly killed him. Sadly, Quantum's gambit kind of throws everything he said out the door with the exception of night 2.
Ah, good call. Traube may have a point then. It makes it difficult to be certain about anything that happened with his switches after he role claimed. I feel like he wouldn't have any reason to lie about anything prior to that though.