http://ruionwriting.net/2011/06/cannot-move-dialog-windows-on-gnome-3/
here are those who hate, other who love and others that really don’t care why dialog windows have strange borders and don’t allow you to move them grabbing the title bar, oh wait 
, where is the title bar?
The solution is simple: gconf-editor to the rescue. Just open gconf-editor and untick /desktop/gnome/shell/windows/attach_modal_dialogs. Press Alt + F2, type r and press Enter (reloads gnome shell). Now you have the normal behavior back.
In case of using Arch, my home distro in this case, you need to install gconf-editor. Very easy with pacman:
$ sudo pacman -S gconf-editor
or
# pacman -S gconf-editor
…
Myself, with Fedora, used
# sudo yum install gconf-editor
And followed the rest of the instructions…
