Version:           1.9.9 (using 3.5.8 "release 44.1" , openSUSE )
Compiler:          Target: i586-suse-linux
OS:                Linux (i686) release 2.6.22.17-0.1-default

Trying to use "delete attachment" from a mail (mail is inside local maildir mailbox) brings up a dialog "Deleting an attachment might invalidate any digital signature on this message." but clicking "OK" only closes the dialog. The mail stays unchanged and still has its attachment.
Some message headers:

MIME-Version: 1.0
Content-Type: multipart/mixed;
  boundary="----_=_NextPart_001_01C87B30.4832E200"


This is a multi-part message in MIME format.

------_=_NextPart_001_01C87B30.4832E200
Content-Type: multipart/alternative;
	boundary="----_=_NextPart_002_01C87B30.4832E200"


------_=_NextPart_002_01C87B30.4832E200
Content-Type: text/plain;
	charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

Dear All,
...


------_=_NextPart_002_01C87B30.4832E200
Content-Type: text/html;
	charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

...


------_=_NextPart_002_01C87B30.4832E200--

------_=_NextPart_001_01C87B30.4832E200
Content-Type: application/vnd.ms-powerpoint;
	name="Demo.ppt"
Content-Transfer-Encoding: base64
Content-Description: Demo.ppt
Content-Disposition: attachment;
	filename="Demo.ppt"

...