The wiping of the post cache isn’t supposed to happen at all when clicking the back button. Didn’t happen prior to June IIRC, so something must have happened to trigger the error handling in Cache Enabler- might have to query them.
Post content is also wiped when this error crops up (also see private sandbox thread):
Error
This page can’t be displayed – your request has been denied for security reasons.
The incident ID is: XXXXXXXXXXXXXXXX
