I think this change:

2006-09-06  Kim F. Storm  <storm@cua.dk>

	* xdisp.c (pos_visible_p): Remove exact_mode_line_heights_p arg;
	so calculate heights even when pos-visible-in-window-p is called
	with partially = t.  Don't overshoot last_visible_y in move_it_to.
	Return row height and row number in new rowh and vpos args.
	(cursor_row_fully_visible_p): First line is always "fully visible".
	(try_window): Don't clear matrix if vscrolled.

introduced a bug in one-line windows (i.e. minibuffer). Especially the
part « Don't overshoot ... ».

- Test case:
emacs -Q
M-x set-variable RET window-min-height RET 1 RET
Make the buffer empty and the window 1 line.
type « kungfu ». Use M-: (pos-visible-in-window-p nil nil t) on
different points :
o C-a (bob) -> (0 0)
o on the `g' -> (21 0)
o C-e (eob (there's no \n)) -> nil

This is due to move_it_to that returns an `it' with 1 as its
IT_CHARPOS on single-line windows.

- I propose the following change (revert):