The problem happens if a user logged in to Bamboo keeps the web console open in the browser and without use for approximately one hour. After this time frame, if the user try to use any of the console options, the page is refreshed and the Login page is displayed on the top of the page that the user was trying to use.

The problem happens only if Bamboo is installed in a Tomcat application server.

Please, see the workaround described in this KB Article