Same as BobH, I have had a couple new and older brushes split the ferrule by soaking in over-hot water. I also had a favorite Omega of years that spit out its knot from the hot water soak.
Some swelling will occur and that was figured in by the makers, A special knot in a expensive handle may have been placed into a metal cup, or tube which can take a lot of swelling. The thickens of the ferrule around the knot and its material can make a big difference. A re-knotted handle may have more swelling than the original smaller knot caused. So there is less material hoop strength of the thinner material to contain the pressure.
JMO
~Richard