omg, I can't stop laughing. I just tried it out and it does gives an error! How did you find this error?
Every time you change the slider value, Alfresco calls /preferences endpoint for the logged in user, with a new value for galleryColumns. It tries to modify the cmerson node, and when you move the slider too fast, it gives concurrency error when writing to database.
Answering your original question... I have no idea how you could solve this error... Maybe overriding the slider change event listener, customize it and filter the calls to preferences endpoint to avoid concurrency errors.