[Sony Cross-Device General] hamfactorial:
I'm attempting to install 2.8.5 to my Z3 Compact. I was running rooted KitKat until a few days ago, then installed the pre-rooted USA Lollipop ROM (23.1.A.0.690) available here.

I had no trouble running that ROM, but tried to run the 2.8.5 installer this morning. I rebooted, saw the red LED light and tried the installer again. Here's the output -

==============================================
= =
= PhilZ Touch, CWM and TWRP Dual Recovery =
= Maintained by [NUT] =
= =
= For Many Sony Xperia Devices! =
= =
==============================================

1. Installation on ROM rooted with SuperSU
2. Installation on ROM rooted with SuperUser
3. Installation on unrooted ROM using the TowelRoot method
4. Install ADB drivers to windows
5. Exit

Please choose install action.
[1,2,3,4,5]?1
* daemon not running. starting it now on port 5037 *
* daemon started successfully *

=============================================
Waiting for Device, connect USB cable now...
=============================================
Device found!

=============================================
Getting ro.build.product
=============================================
Device model is D5803
Firmware is 23.1.A.0.690

=============================================
Step2 : Sending the recovery files.
=============================================
0 KB/s (30 bytes in 0.031s)
2364 KB/s (16947 bytes in 0.007s)
69 KB/s (501 bytes in 0.007s)
1662 KB/s (11920 bytes in 0.007s)
3264 KB/s (56834 bytes in 0.017s)
1003 KB/s (3082 bytes in 0.003s)
1962 KB/s (30148 bytes in 0.015s)
162 KB/s (1162 bytes in 0.007s)
2103 KB/s (34473 bytes in 0.016s)
150 KB/s (924 bytes in 0.006s)
1474 KB/s (13592 bytes in 0.009s)
187 KB/s (385 bytes in 0.002s)
3002 KB/s (719520 bytes in 0.234s)
2915 KB/s (3415689 bytes in 1.144s)
4115 KB/s (2313716 bytes in 0.549s)
3127 KB/s (1934652 bytes in 0.604s)
869 KB/s (8902 bytes in 0.010s)

=============================================
Step3 : Setup of dual recovery.
=============================================
Look at your device and grant supersu access!
Press any key to continue AFTER granting root access.
-rwxr-xr-x 1 shell shell 719520 Apr 8 05:31 /data/local/tmp/recovery/busybox
Press any key to continue . . .

##########################################################
#
# Installing XZDR version 2.8.5 RELEASE
#
#####

Temporarily disabling the RIC service, remount rootfs and /system writable to allow installation.
mount: permission denied (are you root?)
Copy recovery files to system.
Copy chargemon script to system.
Copy dualrecovery.sh to system.
Copy rickiller.sh to system.
Installing NDRUtils to system.
Copy disableric to system.
Copy busybox to system.
Trying to find and update the gpio-keys event node.
Found and will be using /dev/input/event3!
Trying to find and update the power key event node.
Found and will be monitoring /dev/input/event2!
Speeding up backups.
mkdir: can't create directory '/sdcard1/clockworkmod/': Read-only file system
touch: /sdcard1/clockworkmod/.hidenandroidprogress: No such file or directory
Make sure firstboot goes to recovery.

=============================================
DEVICE WILL NOW TRY A DATA SAFE REBOOT!
=============================================

=============================================
Your installation has already cleaned up after
itself if you see the install.bat/install.sh exit.
=============================================

=============================================
Installation finished. Enjoy the recoveries!
=============================================

Press any key to continue . . .

The /system remount seems to be failing, and I've verified that I can't remount R/W via ADB. Previous to running the installer, I had no trouble mounting R/W.