Cache clears even though "Empty Cache" unchecked

I have a site where I have a issue with the cache clearing even though i'm trying to leave it intact (and refresh with cron every night).

I tried both CacheMaster and Form Customization to set the "Empty Cache" check box on the resources unchecked - but in both cases it seems that the cache gets cleared on every save anyway. The install is a 2.2.6 on a modx cloud server.

Does anyone have a suggestion to what might be wrong?