Before - The knife would be out 24/7, unlike Vagabond. Therefore, the concept of "Tele-knifing" (teleport through an enemy while invisible and kill them) was possible. If you plan on resorting to what is shown in this video which is about... 4 years old? Then we'll end up being a flame predator that can just go permanently invisible rather than jump around like a Vagabond.
Soultion? When we do go invisible as vagalion - keep knife out at all times and restrict all weapons on the race.
OR
Rapscallion's knife and Vagabond's knife will have to be removed when invisible as well. It wouldn't be fair in the Vagalion to have it's knife removed and Vagabond can still teleport around knifing with ease, as Tele-knifing on Vagabond is still quite possible, its just a pain in the ass to do. And as for Rapscallion getting its knife removed when it goes invisible, well.... then it just becomes a stationary flame predator that loses its point in camping. I understand Vagalion has a chance for +knife dmg as well but ever since you changed the necklace to where the radius effecting players is greater and we can't stare at somebody and teleport at them directly now (50/50 chance, still get stuck either way), its still a knife race that has to get up close and personal rather than the vagabond with the scout picking people off.
This is my take on the whole "no-knife when invisible" thing. I'll still play it either way.