reported on the forums, but on a wrong thread, so not linking to it
Create a password protected room on a server. Try connecting to it in Spark. Enter wrong password. Click OK in a shown error message. Try connecting to this room and now provide the correct password. Should be able to chat, etc. Unplug network cable or turn off wifi connection. Wait for Spark to start reconnecting. Plug cable back or turn on connection. After successful reconnection Spark will show same error message (wrong password). Click OK in this dialog. You should be logged into room with your old nickname and number 4 appended to it. Try sending a message to the room. Two same messages will appear, one from regular nickname and one from nickname with 4 appended. On the other side users will only see a message sent from nickname with 4 appended.
This only happens with password protected rooms. And only if you have entered wrong password on first attempt. One can restart Spark and enter correct password to fix this issue. Sometimes it appends different numbers, like 7, usually 4 though.