If you desire to downgrade your firmware to UI5:
http://download.mios.com/rt3662_betafirmware/rt3662_Luup_ui5-1.5.622-en-mios.squashfs
Unfortunately, I have become an UI6 victim as well !! Thanks to this thread that I managed to downgrade to UI5. However, VeraLite is auto-upgrading to UI6 and I am back to square one !!.
After my 8th downgrade attempt, i figured out that after a successful downgrade vera is rebooting & auto-upgrading to UI 6. So it appeared as if the downgrade to UI5 never happened.
The only way i can stop the auto-upgrade behaviour is to switch off Internet to Vera. So I am in UI5 now but with no internet access to Vera (and hence no remote access)
Has any one faced this issue ? How do i turn off the auto upgrade of Vera ? I don't know what job/process is causing it and how to stop the same ?
Here is how the downgrade worked for me
1. On UI 6, go to Advanced settings and logged in with my existing (cp.mios) login
2. Took a UI 6 Backup (incl. Z-Wave Network)
3. On the firmware section pasted the link "
http://download.mios.com/rt3662_betafirmware/rt3662_Luup_ui5-1.5.622-en-mios.squashfs" and clicked download. Once the firmware is downloaded i switched off internet to vera (not LAN)
4. Vera rebooted with UI5 blank page. restored the backup in step 2 and i am back to business with all my devices, scenes & apps (UI6 Backup seems to work in UI5)
Now, If i plug back internet VeraLite immediately detects the 'internet' somehow. It reboots and after 10-15 mins I am back to UI6 again !!
Here is output of 'top' command showing list of jobs running on vera right after a reboot (rebooted from UI5 as soon as i plugged in internet). I can't make out what is causing the auto-upgrade and how to stop it

PID PPID USER STAT VSZ %MEM %CPU COMMAND
3803 1 root S 748 1% 1% /usr/bin/luci-bwc -d
4035 4012 root R 1680 3% 0% top
480 1 root S 1928 3% 0% syslogd -C256
3737 3710 root S 1800 3% 0% /bin/sh /usr/bin/SetupRemoteAccess.sh
3710 1 root S 1800 3% 0% /bin/sh /usr/bin/SetupRemoteAccess.sh
3143 2976 root S 1788 3% 0% /bin/sh /usr/share/udhcpc/default.scr
3288 3211 root S 1728 3% 0% /bin/sh /sbin/hotplug-call iface
404 402 root S 1716 3% 0% /bin/sh /etc/init.d/rcS S boot
3835 404 root S 1716 3% 0% /bin/sh /etc/rc.common /etc/rc.d/S98-
3211 3143 root S 1712 3% 0% /bin/sh /sbin/hotplug-call iface
402 1 root S 1712 3% 0% /bin/sh /etc/init.d/rcS S boot
3734 1 root S 1696 3% 0% crond -c /etc/crontabs -l 5
2976 1 root S 1688 3% 0% udhcpc -t 0 -i eth0:0 -r 10.0.0.105 -
1 0 root S 1684 3% 0% init
4012 3979 root S 1684 3% 0% -ash
403 1 root S 1684 3% 0% init
3894 3835 root S 1680 3% 0% /bin/sh /usr/bin/UpdatePackage.sh lua
3834 1 root S 1680 3% 0% watchdog -t 5 /dev/watchdog
405 402 root S 1676 3% 0% logger -s -p 6 -t sysinit
4186 3288 root S 1676 3% 0% rdate -s time-a.nist.gov
I am now out of remote access to my fully automated home of 50+ devices !! Any help here will be appreciated. I tried to search but found nothing for this issue. HELP PLEASE !!