bbdb.el contains :
(defvar bbdb-use-pop-up 'horiz
^^^^^
"If true, display a continuously-updating bbdb window while in VM, MH,
RMAIL, or GNUS. If 'horiz, stack the window horizontally if there is room.")
which contradicts the 'Customization Parameters' node in bbdb.info
`bbdb-use-pop-up'
If true (the default), display a continuously-updating BBDB
^^^^ ^^^^^^^
window while in VM, MH, RMAIL, or GNUS. Each time a new message
is selected, the record corresponding to that message's sender
will be displayed in another window. The buffer in this other
window will be in bbdb-mode, and all corresponding commands will
be available.
