SBCL 2.3.11: Core dump after typing Control-4

SBCL Maintainers,

   I have not been able to find the following documented
anywhere in the SBCL documentation (I have looked in the man
page, the Info file included with SBCL version 2.3.11, and
the latest manual at
https://sbcl.sourceforge.io/manual/index.html) or from a
search of the sbcl-help mailing list archives at 
https://sourceforge.net/p/sbcl/mailman/sbcl-help/.

If I start SBCL from a shell prompt with:

  sbcl --no-user-init

and then type Ctrl-4 (Control key plus the digit 4) at the
initial REPL prompt, then the characters ^\ appear and
shortly after that, SBCL exits with the message:

   Quit (core dumped)

I have been able to reproduce this through numerous restarts
of SBCL.

Is this expected behavior, and if so, is it a documented
feature or is it undocumented?  My search of the SBCL
documents only found Control-D and Control-C mentioned as
documented key bindings.

-- 
The lyf so short, the craft so long to lerne.
- Geoffrey Chaucer, The Parliament of Birds.