can't disable Alt+Button1 shortcut for moving windows around

[Krzysztof Klimonda]

trying to modify the Move Window -> Initiate Window Move value doesn't work, in fact it gets reverted to Alt+Button1 if disabled, otherwise the new value sticks, but is silently ignored.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: unity 7.1.2+14.04.20131106.1-0ubuntu2
ProcVersionSignature: Ubuntu 3.13.0-5.20-generic 3.13.0
Uname: Linux 3.13.0-5-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.13.2-0ubuntu2
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CurrentDesktop: Unity
Date: Tue Jan 28 14:43:27 2014
InstallationDate: Installed on 2014-01-26 (1 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140124)
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)