Using cellular when wifi is enabled.

[Andsoeg]

I have both wifi and Cellular enabled at any time.
Under specific circumstances (Wifi connected but no internet access) it will just use mobile data without noticing me. Wifi logo is at the top just as if i were connected to wifi. I dont know if this is just a setting. I suppose you can test this by pulling out ethernet from your router be connected but still have Cellular enabled. If you can access the internet it is ising Cellular.

[Nexolight]

If so then this is probably a cyanogenmod bug or feature.
It might be possible to change this behaviour

[Mygod]

It's an Android feature since 5.0.