I just reinstalled the lastest ROM (Marshmallow) from my carrier and I found the wifi won't enable during plane mode. It even prompts (only the first time) me that wifi gets turned off when I switch on airplane mode but should I wish to use wifi I can just go ahead and turn it back on. I used it for a couple days as normal after last time I installed the same ROM, same problem but I swear it fixed itself without me doing anything purposefully. Now after the resintall it is back... So I wonder, what the heck is actually going on? Sorry if I lack any more useful info here, I try to reply asap!
Self update: I found the solution in https://android.stackexchange.com/qu...h-wifi-on-only
Looks like my ROM had the wrong setting about airplane mode radio and all you need is adb to correct those settings. You can even tune radio so they do not get disabled when you enable airplane mode. Very nice solution which helped me out! Still does not explain how it was fixed on its own before though. Arh whatever, it is repaired now!