[ICECOLDKILLAK8]

When you crash out of the game or leave the game without typing /quit then the server dosent know you want to disconnect, So it trys to reconnect to you, It takes about 30-40 seconds for the server to realise you have gone, If the client cant connect to the server either then it will try to reconnect, If you or the client try to reconnect before the server has acknowledged your disconnect then it will say Bad Nickname as it thinks you have the same Nickname as another player (Your old connection), Also AFAIK the port you use to connect with is randomised each time you connect so its okay that its changes

Does this happen on other servers or just your own?