interlaced GIF isn't displayed

[Alan]

According to "vm-version.el" I am using version 7.19. I haven't yet
been motivated to change to a newer version. The package index says

* vm 8.07 7.25 An Emacs mailer.

So I could easily upgrade.

I suspect that the experience that I am going to report wouldn't be
affected by upgrading.

My xemacs version is

XEmacs 21.4 (patch 21) "Educational Television" [Lucid] (i586-pc-
win32) of Sun Oct 07 2007 on VSHELTON-PC2

I had someone send me an email which when viewed in another email
client showed text superimposed on a background image. In VM the
image didn't show; instead the complaint was

Unknown/Bad GIF image encoding

I extracted the image to PhotoShop and then made a copy. I was
offered the choice of normal row order or interlaced row order. With
normal row order and the copied image inserted into the email in place
of the original (properly encoded), the image displayed. With
interlaced row order and the copied image inserted into the email in
place of the original (properly encoded), the image was not displayed
and the complaint shown above appeared.

I am not really expecting anyone to fix this. However, others might
appreciate knowing of this behavior.