jar files won't open in emacs 27.1 on debian 11.6 "bullseye"

[Steinar Bang]

Platform: amd64
          debian 11.6 "bullseye"
          GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24, 
cairo version 1.16.0) of 2023-02-23, modified by Debian
          unzip 6.0-26+deb11u1
          libbz2 1.0.8-4

I tried opening some jar files yesterday. I expected them to open in
unzip mode and show the "directory listing" of the jar file contents
(jar files are zip files).

But of these files:
  -rw-r--r--  1 sb sb  52055 Apr  1 20:41 modelstore.backend-1.0.0-SNAPSHOT.jar
  -rw-r--r--  1 sb sb 455179 Apr  1 20:41 
modelstore.backend-1.0.0-SNAPSHOT-javadoc.jar
  -rw-r--r--  1 sb sb  28639 Apr  1 20:41 
modelstore.backend-1.0.0-SNAPSHOT-sources.jar

The modelstore.backend-1.0.0-SNAPSHOT.jar and the
modelstore.backend-1.0.0-SNAPSHOT-sources.jar file opened showing just
the following contents:
M Filemode      Length  Date         Time      File
- ----------  --------  -----------  --------  --------
- ----------  --------  -----------  --------  --------
                     0                         0 files

The modelstore.backend-1.0.0-SNAPSHOT-javadoc.jar files just gives the
following error message, and doesn't open:
File mode specification error: (args-out-of-range 
modelstore.backend-1.0.0-SNAPSHOT-javadoc.jar 445526 445530)

Any idea of how to debug this?
Alternatively, does someone recognize this behaviour and have a workaround?

Does the zip support of emacs 27.1 come in the form of running unzip in
a sub-process? Or does it use a linked in library? (libbz2...?)

Thanks!


- Steinar