I'm using a very recent build of emacs from source:

  GNU Emacs 24.3.50.1 (x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2013-04-27 on dex, modified by Debian
 (emacs-snapshot package, version 2:20130427-1)
Windowing system distributor `The X.Org Foundation', version 11.0.11204000
System Description:	Debian GNU/Linux 7.0 (wheezy)

VHDL mode sets up many of its own key bindings. Two of these bindings
aren't really VHDL specific, but rather represent user preferences:

    (define-key vhdl-mode-map [delete]	     'delete-char)
    (define-key vhdl-mode-map [(meta delete)] 'kill-word))

These redefine the behaviour of DEL and M-DEL in VHDL mode in a way
that's not specific to VHDL. The new behavior of M-DEL is different from
the emacs default, which is to kill backward, not forward. There's no
reason to have this in VHDL mode, and it acts only to surprise users
with non-convention behavior.

The attached patch removes these bindings.