When changing the grid/rotation/snap settings in the viewport preferences, if you press set as default it duplicates everything that is al;ready in the list. For example, if you list of rotation snap settings contains 12 elements, it will double modify the list so that it has 24 elements.
Hi ,
I was able to successfully reproduce this on our end and have entered a bug report for it to be assessed. Thank you for bringing this to our attention!