Package: dpkg
Version: 1.20.9
Severity: bug
In Debian Bullseye dpkg-deb returns nothing when asked for some 'source:*'
field, even if .deb file provides the package that is already installed.
At the same time, dpkg-query output is OK.
Logs from Debian Bullseye chroot:
```
(chr-bullseye-amd64)ubely:~$ sudo dpkg -l | grep "ca-certificates"
ii ca-certificates 20210119 all Common CA certificates
(chr-bullseye-amd64)ubely:~$ dpkg-deb --show --showformat '${Package}' /var/
cache/apt/archives/ca-certificates_20210119_all.deb; echo
ca-certificates
(chr-bullseye-amd64)ubely:~$ dpkg-deb --show --showformat '${source:Package}'
/var/cache/apt/archives/ca-certificates_20210119_all.deb; echo
(chr-bullseye-amd64)ubely:~$ dpkg-query --show --showformat='$
{source:Package}' ca-certificates; echo
ca-certificates
(chr-bullseye-amd64)ubely:~$ dpkg-deb --version
Debian 'dpkg-deb' package archive backend version 1.20.9 (amd64).
```
Under Debign Buster everything is OK:
```
(chr-buster-amd64)ubely:~$ sudo dpkg -l | grep "ca-certificates"
ii ca-certificates 20200601~deb10u2 all Common CA certificates
(chr-buster-amd64)ubely:~$ dpkg-deb --show --showformat '${Package}' /var/
cache/apt/archives/ca-certificates_20200601~deb10u2_all.deb; echoca-
certificates
(chr-buster-amd64)ubely:~$ dpkg-deb --show --showformat '${source:Package}' /
var/cache/apt/archives/ca-certificates_20200601~deb10u2_all.deb; echo
ca-certificates
(chr-buster-amd64)ubely:~$ dpkg-query --show --showformat='${source:Package}'
ca-certificates; echo
ca-certificates
(chr-buster-amd64)ubely:~$ dpkg-deb --version
Debian 'dpkg-deb' package archive backend version 1.19.7 (amd64).
```
