Hi, Bastien, 

Here is a recipe for the bug where scheduling hangs.

1. Change the load path entry in `setup.el'.

2. Start Emacs with `emacs -Q -l setup.el'.

3. Open a TODO list with `M-x org-todo-list'.

4. Filter out tag with `C-u / TAB foo RET'.

5. Move point to first item with `C-s todo RET'.

6. Schedule it for today with `C-c C-s RET'.

An indication that it was scheduled appears in the echo area:

,----
| Scheduled to <2014-05-25 Sun>
`----

But the calendar window remains until you press `C-g'.

Best,

Thomas