*911 Problem...change in how session cookie is being utilized or stored...driving me and the customer's staff batty, constant log outs.

On a client's website (which has been running fine for several years using cmsb), version was 3.64 but now is 3.66 (after trying to figure out this cookie challenge).  What started happening recently and unexpectedly is the cmsb kept logging out whenever we would shift screens.  Normally we can open cmsb in one browser window and the public website in another browser window and shift back and forth between the browser tabs as we make changes on the backend in cmsb and view them live.  What started happening recently is the system logs us out of cmsb the moment we leave that particular tab (to see the other open tab results) we get logged out.  Doesn't seem to matter what location we try this at (I was thinking something on their corporate network might be interfering except that it happens at my home office as well...in any recent browser and different ISPs.  

Upon investigating I noticed on the General Settings page in cmsb there is a cookie prefix that has been entered. I did not enter this and don't know who did.  I am UNABLE to erase it.  I will delete, save the page, go to another page/tab and have to log back in...and voila! the same cookie prefix has reappeared.  This is repeatable...and is 100% repeatable and problematic.  

A screenshot of the General Settings page, where the cookie prefix displays, is included here. 

Thank you kindly for your assistance.