Undoing port deletion causes wrong drawn channel
(Reproduced on SimpleTrafficLightsExample)
Deleting a port correctly deletes the connected channel, after pressing
Cmd-Z to restore the port, the channel is also restored, but drawn not
from the source port but from the left upper angle of the window.
Closing and re-opening the window resolves the drawing error.
(from redmine: issue id 968, created on 2012-08-24, closed on 2014-07-28)