This was an issue that appeared with v0.19, and that has been corrected in our most recent release v0.20. If your Shake is connected to the internet, it will automatically download and install the new OS version during this week, otherwise, the v0.20 image will be made available later in the month.
Thank you for taking the time of communicating this to us, and for your patience in the matter.
The wpa_supplicant file you copy to the boot partition is not static. It is processed on boot and deleted after it updates your network configuration. All Raspberry Pi’s and other small boards do this. It is just a way to setup your wireless connection without having to SSH in to edit configuration files. On boards without an ethernet connection, it makes it a lot easier to configure your WiFi settings.