The header part of a frame cannot be read from the data source. When using in Unity

I have a websocket server Windows Form app using the github version here and a unity client using the asset store version.

Whenever I press play in unity it works perfectly but when I stop playing, then try play again, it gives me this:

Exception thrown: 'WebSocketSharp.WebSocketException' in websocket-sharp.dll
20/11/2015 5:23:21 PM|Fatal|WebSocket.processException:1017|WebSocketSharp.WebSocketException: The header part of a frame cannot be read from the data source.
at WebSocketSharp.WebSocketFrame.processHeader(Byte[] header) in C:\Work\Bugpunch\websocket-sharp\websocket-sharp\WebSocketFrame.cs:line 444
at WebSocketSharp.WebSocketFrame.<>c__DisplayClass75_0.b__0(Byte[] bytes) in C:\Work\Bugpunch\websocket-sharp\websocket-sharp\WebSocketFrame.cs:line 540
at WebSocketSharp.Ext.<>c__DisplayClass47_0.b__0(IAsyncResult ar) in C:\Work\Bugpunch\websocket-sharp\websocket-sharp\Ext.cs:line 629
20/11/2015 5:23:21 PM|Error|WebSocketBehavior.Start:345|This session has already been started.

Reproduce the Unity stop-and-play-again cycle, then start with WebSocketFrame.cs at lines 444 and 540, Ext.cs at line 629, and WebSocketBehavior.Start at line 345. Trace the session and frame-reading lifecycle to determine why the second run reaches these errors; done means the repeated play cycle no longer produces the reported exception or already-started session error.