On Cinnamon 1.6.7 / Gnome 3.6.2, dragging the steam windows have a normal behavior if the window already has focus, but when the title bar area is clicked to give the window focus, the mouse remains in the move window state for me until the mouse is clicked again. Personally, I would not describe this as a window manager issue.
Oh yeah, that's another thing that's happened to me, although only some of the time and not since I installed the latest 64-bit build from scratch, so far. It seemed to especially happen for pop-up windows like the "Preparing to launch" one, but maybe that's just coincidence.
How do you disable this "Transparent when drag" feature? It's messing up my seamless desktop under VirtualBox.
Nothing extracted yet.
In KDE 4.x, windows become semi-transparent when dragged or resized. In order to keep this from being annoying in cases where the user is merely clicking the titlebar to focus it, there's a delay of about half a second of the mouse button being held down. Except in the Steam client's windows, where it happens immediately. This is especially annoying for the main window, because its draggable area is much larger than the actual titlebar.
I know KDE isn't officially supported yet, but I'm seeing other KDE-specific issues staying open on here, so I figured I'd throw this one on the pile.