`move-beginning-of-line' doesn't move to beginning of line

[Chris Moore]

In *shell* buffers, "C-h k C-a" tells me that:

  C-a runs the command move-beginning-of-line
  Move point to beginning of current line as displayed.

However, when I hit C-a, the cursor stays at the end of the prompt,
not at the beginning of the line.  This may be desired behaviour
(although I find it annoying; I often want to go to the beginning of
the prompt) but it isn't the documented behaviour.  The documentation
should match the behaviour one way or the other.

In GNU Emacs 22.0.96.2 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2007-03-20 on trpaslik
Windowing system distributor `The X.Org Foundation', version 11.0.70101000
configured using `configure  '--with-gtk' '--prefix' '/usr/local' '--with-xpm' 
'--with-jpeg' '--with-png' '--with-gif''