The only way that could happen is if you deleted the local.gbf file or it failed to create one when it patched. This is possible.
Sorry it hurt but I am sure you could have removed your headphones before your ears popped.
Settings were getting changed and it was in the patch notes. This should have alerted you to the fact that the sound setting could reset. It could reset at any time much like any media player could start at 100% volume every time you open it.
The Devs make every effort and the settings reset issue seems to only have effected a few people and not everyone. That's good at least.
Less Q.Q and threats of suing and more being a man.
The Game