“Clear full cache when post/page is updated” setting lost

I have an on-going issue with a number of site I manage. The setting “Clear full cache when post/page is updated” gets turned off after a period of time. This keeps happening and it’s getting to be rather an issue.

My client reported blogs not appearing on the homepage on Wednesday, I checked and saw that “Clear full cache when post/page is updated” had become unset, so I set it again. All was well yesterday but I’ve checked again today and it’s been unset again. It happens on many sites, so I don’t think environment-specific