zathura and ownership of files in /proc/PID

Yesterday, while writing an answer to [How to get full path names of all opened pdf files (in zathura) - like rofi does](https://unix.stackexchange.com/questions/741457/how-to-get-full-path-names-of-all-opened-pdf-files-in-zathura-like-rofi-does) , I noticed something weird about the ownership of files the /proc/PID/ directory for zathura processes - **most of them are owned by root instead of the user (cas) I ran zathura as**. For example:

$ cd ~/Manuals
$ zathura X399\ Taichi.pdf &
 4055396

$ ls -lF /proc/4055396/fd
ls: cannot open directory '/proc/4055396/fd': Permission denied
$ ls -lFd /proc/4055396/fd
dr-x------ 2 root root 0 Mar 31 13:04 /proc/4055396/fd/

huh? why is that owned by root? I ran it as cas. Most, but not all of the files/dirs in /proc/4055396 are owned by root:

$ ls -lF /proc/4055396
ls: cannot read symbolic link '/proc/4055396/cwd': Permission denied
ls: cannot read symbolic link '/proc/4055396/root': Permission denied
ls: cannot read symbolic link '/proc/4055396/exe': Permission denied
total 0
-r--r--r--  1 root root 0 Mar 31 13:04 arch_status
dr-xr-xr-x  2 cas  cas  0 Mar 31 13:04 attr/
-rw-r--r--  1 root root 0 Mar 31 13:04 autogroup
-r--------  1 root root 0 Mar 31 13:04 auxv
-r--r--r--  1 root root 0 Mar 31 13:04 cgroup
--w-------  1 root root 0 Mar 31 13:04 clear_refs
-r--r--r--  1 root root 0 Mar 31 13:02 cmdline
-rw-r--r--  1 root root 0 Mar 31 13:04 comm
-rw-r--r--  1 root root 0 Mar 31 13:04 coredump_filter
-r--r--r--  1 root root 0 Mar 31 13:04 cpu_resctrl_groups
-r--r--r--  1 root root 0 Mar 31 13:04 cpuset
lrwxrwxrwx  1 root root 0 Mar 31 13:04 cwd
-r--------  1 root root 0 Mar 31 13:04 environ
lrwxrwxrwx  1 root root 0 Mar 31 13:02 exe
dr-x------  2 root root 0 Mar 31 13:04 fd/
dr-xr-xr-x  2 cas  cas  0 Mar 31 13:04 fdinfo/
-rw-r--r--  1 root root 0 Mar 31 13:04 gid_map
-r--------  1 root root 0 Mar 31 13:04 io
-r--------  1 root root 0 Mar 31 13:04 ksm_merging_pages
-r--------  1 root root 0 Mar 31 13:04 ksm_stat
-r--r--r--  1 root root 0 Mar 31 13:04 limits
-rw-r--r--  1 root root 0 Mar 31 13:04 loginuid
dr-x------  2 root root 0 Mar 31 13:04 map_files/
-r--r--r--  1 root root 0 Mar 31 13:04 maps
-rw-------  1 root root 0 Mar 31 13:04 mem
-r--r--r--  1 root root 0 Mar 31 13:04 mountinfo
-r--r--r--  1 root root 0 Mar 31 13:04 mounts
-r--------  1 root root 0 Mar 31 13:04 mountstats
dr-xr-xr-x 57 cas  cas  0 Mar 31 13:04 net/
dr-x--x--x  2 root root 0 Mar 31 13:04 ns/
-r--r--r--  1 root root 0 Mar 31 13:04 numa_maps
-rw-r--r--  1 root root 0 Mar 31 13:04 oom_adj
-r--r--r--  1 root root 0 Mar 31 13:04 oom_score
-rw-r--r--  1 root root 0 Mar 31 13:04 oom_score_adj
-r--------  1 root root 0 Mar 31 13:04 pagemap
-r--------  1 root root 0 Mar 31 13:04 patch_state
-r--------  1 root root 0 Mar 31 13:04 personality
-rw-r--r--  1 root root 0 Mar 31 13:04 projid_map
lrwxrwxrwx  1 root root 0 Mar 31 13:04 root
-rw-r--r--  1 root root 0 Mar 31 13:04 sched
-r--r--r--  1 root root 0 Mar 31 13:04 schedstat
-r--r--r--  1 root root 0 Mar 31 13:04 sessionid
-rw-r--r--  1 root root 0 Mar 31 13:04 setgroups
-r--r--r--  1 root root 0 Mar 31 13:04 smaps
-r--r--r--  1 root root 0 Mar 31 13:04 smaps_rollup
-r--------  1 root root 0 Mar 31 13:04 stack
-r--r--r--  1 root root 0 Mar 31 13:02 stat
-r--r--r--  1 root root 0 Mar 31 13:04 statm
-r--r--r--  1 root root 0 Mar 31 13:04 status
-r--------  1 root root 0 Mar 31 13:04 syscall
dr-xr-xr-x  6 cas  cas  0 Mar 31 13:04 task/
-rw-r--r--  1 root root 0 Mar 31 13:04 timens_offsets
-r--r--r--  1 root root 0 Mar 31 13:04 timers
-rw-rw-rw-  1 root root 0 Mar 31 13:04 timerslack_ns
-rw-r--r--  1 root root 0 Mar 31 13:04 uid_map
-r--r--r--  1 root root 0 Mar 31 13:04 wchan

zathura is NOT setuid root:

$ type -p zathura
/usr/bin/zathura

$ ls -l /usr/bin/zathura
-rwxr-xr-x 1 root root 305456 Nov 28 03:34 /usr/bin/zathura

It is version 0.5.2, and the package was last upgraded on November 28 last year:

$ zathura --version
zathura 0.5.2
girara 0.3.7 (runtime: 0.4.0)
(plugin) cb (0.1.10) (/usr/lib/x86_64-linux-gnu/zathura/libcb.so)
(plugin) pdf-poppler (0.3.1) (/usr/lib/x86_64-linux-gnu/zathura/libpdf-poppler.so)
(plugin) ps (0.2.7) (/usr/lib/x86_64-linux-gnu/zathura/libps.so)
(plugin) djvu (0.2.9) (/usr/lib/x86_64-linux-gnu/zathura/libdjvu.so)

$ dpkg -l zathura
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-=============================================
ii  zathura        0.5.2-1      amd64        document viewer with a minimalistic interface

$ ls -l /var/cache/apt/archives/zathura_0.5.2-1_amd64.deb 
-rw-r--r-- 1 root root 175712 Nov 28 04:41 /var/cache/apt/archives/zathura_0.5.2-1_amd64.deb

If I use qpdfview, atril, or okular instead of zathura, the permissions are fine:

$ qpdfview X399\ Taichi.pdf 
$ pgrep qpdfview
4071588 qpdfview X399 Taichi.pdf
$ ls -lFd /proc/4071588/fd
dr-x------ 2 cas cas 0 Mar 31 13:16 /proc/4071588/fd/

$ atril X399\ Taichi.pdf &
 4080297
$ ls -lFd /proc/4080297/fd
dr-x------ 2 cas cas 0 Mar 31 13:20 /proc/4080297/fd/

$ okular X399\ Taichi.pdf &
 4081710
$ ls -lFd /proc/4081710/fd
dr-x------ 2 cas cas 0 Mar 31 13:21 /proc/4081710/fd/

All of the above were run from the same instance of bash, same environment, same everything. Not in a VM or container, or anything "unusual". So, what is up with zathura? Is it zathura? or is it some weird namespaces related behaviour by systemd or cgroups or something like that? The system is running Debian sid (updated yesterday), with kernel Linux hex 6.1.0-6-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.15-1 (2023-03-05) x86_64 GNU/Linux. The last reboot was 14 days ago when I upgraded the kernel, has been running fine since then. --- NOTE: I vaguely recall that when I was working on my answer yesterday, I saw the same root ownership thing for ONE of the instances of running atril, but I can't replicate that now. I may have mis-remembered this, it was very late at night (> 3am) and I was tired. zathura, however, consistently has root-owned stuff in /proc/PID/ - every time I run it.