Many processes launched by Thunar (e.g., double-click on a picture file and eog is launched) become defunct -- a zombie process after they are closed (e.g., exit from program's menu file/exit).

This doesn't happen all the time, but does happen a lot. Very annoying.

Programs often happen that way: eog, evince, totem -- I see many of those in zombie state since I often double-click on types of files supported by them, and of course the list is not exhaustive.

As a side note, sometimes this happen to programs launched from xfce's terminal program (mainly make and subsequent programs such as gcc, more makes, autom4te etc.), maybe it is because it uses some common library as Thunar to launch external programs?