I agree its a rare thing however you never know when it will happen and there aren't any warning signs all the time. Sometimes it will just start in a tiny spot and quickly worsen. Also many times its not the old beat up scales that start to degrade its the nice pristine mint looking ones.

However its not a reason to avoid celluloid. Just be aware and inspect your razors on a regular basis and you will be fine. If it happens just quarantine the razor and trash the scales.