This issue affects only bttns running firmware version March 2015 (20150300 and 20150302).
When you enter your Wi-Fi settings on the bttn's internal website (192.168.0.1/bttn), and choose open network, the bttn doesn't restart itself automatically after clicking "save".
The settings are stored, but the restart must be done manually - i.e. please just remove power for a couple of seconds and then re-insert.
Please note that in open network's name (SSID) you still cannot have special characters.
This issue has been fixed in firmware version June 2015 (20150602).