\showstream oddity

Hello all,

We've just spotted an oddity with \showstream. Consider the example

\immediate\openout1=test.txt
\immediate\write1{test}
%\showstream1   % A real file
%\showstream16  % or 128 for LuaTeX
\show\foo
\immediate\write\showstream{^^Jbong}
\bye

With the file as-is, the \show output appears in the terminal and the 
log, but the \write only goes to the (log the standard setting for 
\showstream is -1). Setting \showstream to 1 sends everything to the 
real file, and to 16 (or in LuaTeX 128) sends everything to the terminal.

The default behaviour is puzzling. It seems that \show more-or-less 
ignores \showstream there, or special cases, as it does *not* only send 
to the .log. My feeling is that the engines should be setting 
\showstream to a default that gives predictable but unchanged behaviour 
(e.g. 16+ or LuaTeX 128+) - but there is an alternative interpretation.

Regards,

Joseph