Same problem here, after the update all files on SDCard have root:root owner and are only writable by the owner (i.e. root). I can write there as root without problem. But non-elavated apps cannot write there (e.g. camera) which results in very weird behaviour (e.g. camera app freezing). Fsck shows no problem. It's VFAT so there are no permissions in the FS. It seems /media/mmc1 is automounted by some daemon (I wasn't able to find it yet) on first access and it mounts it as wrong owner.