RE: Unable to match octal character

[Drew Adams]

> > I have a file with some characters that display in the emacs buffer as
> > \203.  Yet when I search for that, using C-s C-q 203 <ret> I can't match
> > it.  Likewise if I use search and replace.
> 
> Works for me.  Do you see the same thing if you start Emacs using
> `emacs -Q' (no init file)?
> 
> YES

So you see the same problem even without your init file.
But when you do it in *scratch* (below) you don't see the problem.

> What happens if you do this, starting from emacs -Q:
> 1. In *scratch*, move point into the text somewhere and use
>    `C-q 203 RET' to insert the \203 character.
> 2. `M-<'
> 3. `C-s C-q 2 0 3 RET'
> 
> THE SEARCH SUCCEEDS.

Then I guess you will need to explore the difference between
the context where you see the problem, even starting from `emacs -Q',
and the above context (recipe using *scratch*).

Try to provide a step-by-step recipe, which starts from `emacs -Q',
to reproduce the problem.