Custom dual screen configuration buggy

Using Ubuntu's system settings to configure two screens (desktop monitor and TV via HDMI in my case) is not ergonomic.

Hence I decided to code a handy switcher script which lets me choose between mirrored output ("mirror") and either left screen on/right screen off or left screen off/right screen on ("switch"). It is based on xrandr.

It works as expected and I like the flexibility when using xrandr, BUT:

• tearfree setting necessary for TV output is either ignored or ineffective after using my script (Why?)
• system settings are broken after using my script: If I change screen configuration via system settings afterwards, output will be scrambled.

My script must be doing something horribly wrong. How can I make it work correctly?

Script:

#!/bin/bash

DESKTOP="DP1" # desktop monitor
DSIZE="1280x1024"

TVPORT="HDMI1" # connection to TV
TVSIZE="1920x1080"

SCALE="1.5" # e.g. 1920/1280

if xrandr | grep "$TVPORT" | egrep "\)$"
then # TV port is turned OFF => turn it on
  selected_mode=`echo -e "mirror\nswitch" | zenity --list --text="Choose Mode:" --column="Mode"`
  if test "$selected_mode" = "mirror"
  then
    xrandr --output "$TVPORT" --auto --left-of "$DESKTOP" --output "$DESKTOP" --panning "$TVSIZE"
    xrandr --output "$DESKTOP" --scale "$SCALE"x"$SCALE" --mode "$DSIZE" --fb "$TVSIZE" --panning "$TVSIZE"
  fi
  if test "$selected_mode" = "switch"
  then
    xrandr --output "$TVPORT" --auto --output "$DESKTOP" --off
  fi
else # TV port is turned ON => turn it off
  xrandr --output "$TVPORT" --off --output "$DESKTOP" --mode "$DSIZE" --fb "$DSIZE" --scale 1x1 --panning "$DSIZE"
fi

exit 0

Tearfree which works when using Ubuntu normally, but not after running my script:

$ cat /etc/X11/xorg.conf
Section "Device"
   Identifier  "Intel Graphics"
   Driver      "intel"
   Option      "AccelMethod" "sna"
   Option      "SwapbuffersWait" "true"
   Option      "TearFree" "true"
EndSection