Why does "pgrep -O 600" fail in an LXC? procps bug?

Debian 12.2 in an unpriviledged LXC (proxmox). It's almost 11:45 AM local time. At 5:00 AM in the morning, cron started a script: USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND jan 26633 0.0 0.0 8500 2056 ? S 05:00 0:00 /usr/sbin/CRON -f I'm using pgrep -f CRON -O 600 and I expect pgrep to return PID 26633, because the process is way older than 600 seconds. But pgrep returns nothing. If I leave out the -O, it correctly returns the PID. Doing the same on the host machine, i.e. outside of the LXC, it works correctly. As pgrep uses procps, I looked there. ps -o etime -p $pid in the LXC: 441077225-02:04:48 (wrong, because since 5:00, ~6:45h passed) ps -o etime -p $pid on the host: 06:43:29 (correct) Would that be a bug in procps or does it rather have to do with LXC?