We think that this issue was fixed in version 4.89. Could you try it?
We guess this issue cannot resolve.
In normal case, "Undock" from start menu. But Windows does not permit undock while serial port is opened.
Close serial port in Tera Term, undock, dock and connect serial port in Tera Term.
In irregular case, force remove docking station physically. In this case, serial port will not remove from Windows system.
Windows does not receive undock event. Then a program cannot handle this event.