AppVeyor test runs fail with "Only one usage of each socket address is normally permitted"

[IgorMilavec]

Sometimes AppVeyor test runs fail with System.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted.. After one occurrence of this exception, most consequent tests fail with the same exception.
A typical example of such behavior is this build of #855.