Internal storage missing: Nexus 7 16G down to 5.8G TOTAL

Internal storage missing: Nexus 7 16G down to 5.8G TOTAL

My Nexus 7 now believes it has only 5G internal storage. It's shown in
storage properties.
I noticed it after factory reset, and then a 4.3 update (I remember
getting 4.3 OTA update twice, is it possible?)
I installed ClockworkMod recovery (back when it was on 4.2), but never
rooted it.
No storage space analyzers show hidden files or such. Rebooting doesn't
change anything.
I found /sdcard/0 directory with a content of my previous sdcard before a
factory reset, deleting it freed some space, but total is still at 5.8G.
I found one complaint about a similar situation, but it's drowned in a
simpler problems and was never answered.
df output:
Filesystem Size Used Free Blksize
/dev 487.4M 32.0K 487.3M 4096
/mnt/secure 487.4M 0.0K 487.4M 4096
/mnt/asec 487.4M 0.0K 487.4M 4096
/mnt/obb 487.4M 0.0K 487.4M 4096
/system 639.8M 515.7M 124.1M 4096
/cache 436.0M 7.3M 428.7M 4096
/data 5.9G 2.7G 3.2G 4096
/mnt/shell/emulated 5.9G 2.7G 3.2G 4096
/mnt/asec/com.teslacoilsw.launcher.prime-1 2.0M 84.0K 1.9M 4096
/mnt/asec/com.loudcrow.goodnightmoon-1 5.0M 3.4M 1.6M 4096
cat /proc/partitions output:
major minor #blocks name
7 0 2111 loop0
7 1 5229 loop1
179 0 7467008 mmcblk0
179 1 12288 mmcblk0p1
179 2 8192 mmcblk0p2
179 3 665600 mmcblk0p3
179 4 453632 mmcblk0p4
179 5 512 mmcblk0p5
179 6 10240 mmcblk0p6
179 7 5120 mmcblk0p7
179 8 512 mmcblk0p8
179 9 6302720 mmcblk0p9
179 32 2048 mmcblk0boot1
179 16 2048 mmcblk0boot0
254 0 2110 dm-0
254 1 5229 dm-1
mount output:
rootfs / rootfs ro,relatime 0 0
tmpfs /dev tmpfs rw,seclabel,nosuid,relatime,mode=755 0 0
devpts /dev/pts devpts rw,seclabel,relatime,mode=600 0 0
proc /proc proc rw,relatime 0 0
sysfs /sys sysfs rw,seclabel,relatime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,relatime 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
none /acct cgroup rw,relatime,cpuacct 0 0
tmpfs /mnt/secure tmpfs rw,seclabel,relatime,mode=700 0 0
tmpfs /mnt/asec tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
tmpfs /mnt/obb tmpfs rw,seclabel,relatime,mode=755,gid=1000 0 0
none /dev/cpuctl cgroup rw,relatime,cpu 0 0
/dev/block/platform/sdhci-tegra.3/by-name/APP /system ext4
ro,seclabel,relatime,user_xattr,acl,barrier=1,data=ordered 0 0
/dev/block/platform/sdhci-tegra.3/by-name/CAC /cache ext4
rw,seclabel,nosuid,nodev,noatime,errors=panic,user_xattr,acl,barrier=1,nomblk_io_submit,data=ordered
0 0
/dev/block/platform/sdhci-tegra.3/by-name/UDA /data ext4
rw,seclabel,nosuid,nodev,noatime,errors=panic,user_xattr,acl,barrier=1,nomblk_io_submit,data=ordered
0 0
/dev/fuse /mnt/shell/emulated fuse
rw,nosuid,nodev,relatime,user_id=1023,group_id=1023,default_permissions,allow_other
0 0
/dev/block/dm-0 /mnt/asec/com.teslacoilsw.launcher.prime-1 ext4
ro,dirsync,seclabel,nosuid,nodev,noatime,user_xattr,acl,barrier=1 0 0
/dev/block/dm-1 /mnt/asec/com.loudcrow.goodnightmoon-1 ext4
ro,dirsync,seclabel,nosuid,nodev,noatime,user_xattr,acl,barrier=1 0 0