In option to keep tab open on disconnect there is ability to reconnect when host becomes available which I assumes relies on ping to find out if host is available and reconnects.
This needs to be changed to TCP open instead for 2 reasons.
1. PING does not guarantee that RDP is available (like in case of reboot ICMP will be initialized before RDP is available)
2. When ICMP is blocked on destination firewall, this option will never work.
So TCP open with short timeout (like 2 s) will be much better and faster choice as well.
You can change the Online Detection to Port Scan instead of Ping in File -> Options -> General.