Mail body escape sequence fouls display

[Karl Kleinpaste <karl@charcoal.com>]

After a very long hiatus, yesterday I upgraded to XEmacs 21.5.20 and
No Gnus v0.03.

When I get mail which contains literal escape characters in the text,
it can make all text following that point, and all further mail in the
same group, be grey or reverse video.

Specific circumstance is that I have environment variables TERM_SO and
TERM_SE, which contain the libcurses "standout" and "standout end"
(rev video) sequences for the terminal.  An automatic self-mail-
sending function in my shell emails me dumps of my shell state in
terminals, including env.variables.  When these mails are subsequently
seen in Gnus, the literal escape sequence of TERM_SO causes all further
text downward in that email to be rev video.

Weirder still, when reading the _next_ message in the same group,
*all* text is rev video, *except* for the line following the TERM_SE
sequence, which of course turns off rev video in a terminal, but then
(because of the order of the dump) the following TERM_SO turns rev
video back on again.

But the _header_ is never rev video, even in 2nd-thru-Nth items.

Since when does Gnus, or XEmacs in general, react to embedded escape
sequences in text being displayed?  (As opposed to using escape
sequences heavily for terminal control, of course.)

Screenshots...
First message in group, text goes rev video at the TERM_SO:
http://www.charcoal.com/~karl/gnus/screenshots/summary-personal.recall-1.png
Second message, text is rev video from beginning;
http://www.charcoal.com/~karl/gnus/screenshots/summary-personal.recall-2.png

--karl