Looks like ifconfig in the load / unload script for the injection drivers throws up that error message looking for the hardware address of wlan0. With injection drivers loaded it doesn't seem to find the wlan0 device anymore. I am getting a "Unknown symbol in module" error when trying to load wl1251_spi.ko, which might explain why ifconfig doesn't see the hardware (ie. the drivers are not loaded).

Edit: Rebooted a few times and re-downloaded the KP50 version drivers again fixed the problem for a bit, but I have a feeling that they are not really stable; ie. after awhile, the loading / unloading runs into problems again. Might be a solution to just load them and run with them, ie. avoid repeated loading / unloading cycles.