If I Alt-Tab to another window while moving the camera around via middle mouse button, all UI becomes impossible to click on. Trying to move items around in the inventory or trying to craft something through the UI will just have my click ignore the UI and move my character instead. This is always reproducible for me in both default and in amber client. I always use ortho camera.
May or may not be related to this issue, as the problems are the same: viewtopic.php?f=47&t=40541