To reproduce this bug you have to use MITK and the "PLUS Server Launcher" application of the PLUS toolkit (tested with PLUS-versions 2.2.0 | 2.6.0):

--> Establish an active connection between PLUS (server) and MITK (client) exactly as described in Task 1 of the OpenIGTLink checklist.
--> PLUS Server Launcher: Finish the PLUS-Server: click on "Stop Server".
--> As a result: the active connection between PLUS and MITK is interrupted.
--> MITK: However, the tracked tool is still visualized in green color and the button "Stop Tracking" of the TrackingToolbox is still active and can be clicked.
--> PLUS Server Launcher: Restart the PLUS-Server: click on "Launch Server".
--> MITK: The connection to the PLUS-Server remains disconnected even if you click on "Stop Tracking" and then on "Start Tracking" of the TrackingToolbox.
--> MITK: The only way of reestablishing the connection to the PLUS-Server is: Click on "Disconnect" and then on "Connect" of the TrackingToolbox.

This software behavior of MITK could be improved:

Whenever an active OpenIGTLink connection to a server gets lost: Actualize the GUI (+ Buttons of the TrackingToolbox) and inform the user (in a visible way) that the connection is broken.

optional: Establish/Initialize an automatic reconnect mechanism to the server, which tries all X seconds to reconnect to the server. Stop the reconnect mechanism after N unsuccessful reconnect attempts.