bug#20100: 24.4.91; Can't scroll a window while in minibuffer

[Oleh Krehel <ohwoeowho@gmail.com>]

I'm trying to write a completion package using `read-from-minibuffer'
combined with `post-command-hook'.

Everything is working OK, except when I want to sync the current
completion candidate (one of buffer's lines) with the corresponding line
in the buffer.

This code, specifically `recenter', doesn't work:

(with-current-buffer buf
  (goto-char (point-min))
  (forward-line (1- num))
  (recenter))

However, this code will scroll the window (`buf' and `wnd' correspond to
each other):

(with-current-buffer buf
  (goto-char (point-min))
  (forward-line (1- num))
  (setf (window-point wnd)
        (point)))

Still, it's not a perfect solution, since even after setting
`window-point', (window-start wnd) and (window-end wnd t) will not
return the correct thing.

I'm pretty sure it's a bug and the code above should work as is, but I'd
also appreciate pointers for achieving the scrolling and window bounds
re-calculation for the current Emacs.

regards,
Oleh