Originally Posted by gwodus
Thank you so much. I had that problem as well.
There seem to be many other problems which can cause a read only sdcard. I was googling for hours and was trying other stuff. I guess this is a more exotic problem which only happens on Xperias? It happened to me after I upgraded from CM11 to CM12 and then restored CM11 again from a nandroid backup (CWM).
I don't know if it's an "exotic" problem, but AFAIK, it only happens on Xperias because of Sony's stupid decision to use a different user/group for the internal memory.
When you upgraded to CM12, the ownership got changed, then you restored your backup which doesn't fix that, so it makes perfect sense.