Window pane selection inconsistent?

[Alex Dyas]

Hello,

In the key bindings section of the manual it states :

Up, Down
Left, Right
Change to the pane above, below, to the left, or to the right of the
current pane.

However I find the actual behavior to be somewhat inconsistent. Changing to
the pane to the right of the current pane for instance sometimes results in
the pane to the top and right being selected, not the one directly to the
right.

Am I misunderstanding something, or is this a bug?

Setup:
tmux 1.9a, Ubuntu
<.tmux.conf>
set-option -g prefix C-DC
set-window-option -g mode-keys vi
set-option -g history-limit 5000
</>

Thanks,

Alexander