See http://earlruby.org/2012/04/getting-rid-of-self-resizing-windows-in-ubuntu-linux-12-04/
In a nutshell, from the above page:
sudo apt-get install compizconfig-settings-manager Applications > System Tools > Preferences > CompizConfig Settings Manager Click "Window Management" Uncheck “Place Windows”. Click the Grid word (not the Grid checkbox -- leave it checked) Select the Edges tab and change all Resize Actions to “None”.