In QT client the message+chat window is resizeable by dragging the lower right corner.
If by mistake, the player resizes this window and drags the right border more to the left than the left edge, the window just disappears, and never comes back until quit and restart.
In client-gtk one can use F9 to relaunch this window, but this is missing in QT. (maybe this should be added too)
alain_bkr 
In QT client the message+chat window is resizeable by dragging the lower right corner.
If by mistake, the player resizes this window and drags the right border more to the left than the left edge, the window just disappears, and never comes back until quit and restart.
In client-gtk one can use F9 to relaunch this window, but this is missing in QT. (maybe this should be added too)