The Beta UI logs you off after X mins, there is not setting to control that?
I'm not aware of any change here that would cause different behaviour between the current master branch, and the FTLDNS branch of the web... I'll look into it.
It has always been like that. The only exception is when you are on the dash board as this page is constantly updated, constantly refreshing your session. You should be able to see the remaining validity of your current session once you open the menu on the top right. On the dashboard, the counter is continuously reset whenever one of the elements refreshes (this happens quite often).