F6/shift-F6 behavior
Many applications define F6/shift F6 for moving keyboard focus between areas in a window. This doesn't seem true of Gajim.
This helps with accessibility by allowing the contents of chat windows to be accessed as if they were documents. This allows for scrolling with arrows/pgup/pgdn, keyboard selection for cut-n-paste, etc. and a number of other accessibility features that are otherwise more difficult to accomplish.
For a good example of this behavior, see Pidgin 2.5.3 and later. Press F6 in an IM window and you'll shift focus between the chat input and message area. In group chat, the table of group members is also selectable this way.