Mouse pointer can not be moved to the right-bottom edge of an output, if --scale-from resolution exceeds --mode resolution

[Jarno Suni]

Provided you have an output called LVDS1 that is capable to show 1024x768 resolution, after running
xrandr --fb 1154x864 --output LVDS1 --scale-from 1154x864 --mode 1024x768
try to move mouse pointer to the right-bottom edge of the output. It should move there, but it does not.

I want to use the scaling to output to 16:9 TV in right aspect ratio:
xrandr --fb 1024x576 --output LVDS1 --off --output TV1 --scale-from 1024x576 --set mode PAL --mode 800x600
However, if I run
xrandr --fb 1024x576 --output LVDS1 --mode 1024x768 --output TV1 --scale-from 1024x576 --set mode PAL --mode 800x600
mouse pointer can be moved to the bottom-right corner of the TV1 output (minus possible marginals).

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: x11-xserver-utils 7.7+0ubuntu2
ProcVersionSignature: Ubuntu 3.11.0-17.31-generic 3.11.10.3
Uname: Linux 3.11.0-17-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Sun Mar 2 13:16:49 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-09-20 (163 days ago)
InstallationMedia: Lubuntu 13.04 "Raring Ringtail" - Release amd64 (20130423.1)
MarkForUpload: True
SourcePackage: x11-xserver-utils
UpgradeStatus: Upgraded to saucy on 2013-10-18 (134 days ago)