If your experiencing issues with disconnections through Windows 2012 RDS Web Interface and you have already disabled all the idle session limits on your TS Farm by a GPO you might also wish adjust your IIS timeout limits as well.
RDS Web uses HTTPS for RDP so the standard timeout are applied to your RDP connection. In theory it is good practice but I am sure your remote based users will not feel the same.
These settings need changing on your website that hosts RDS
