Sylvain, thanks saving my time :)
For example:
emacs -Q --eval "(progn (toggle-truncate-lines 1) \
(split-window-right) \
(other-window 1) \
(split-window-below) \
(insert \"blahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblah\"))"
Then try to windmove-down, it moves left! :/
window-in-direction seems to be doing fine anyway!
Sylvain.