merged flac files result in incorrect Duration

[lduesing]

Having an "Adventskalender" by ???, with each day a new track, I build every day a new version of the up to date audiobook for my family. I ripped the CD to .flac-files and move the corresponding m4b-file to the nas, so there is every day a complete new version in a clean directory.
All chapters are correct so far:

00:00:00.000                             : Tag 01 Winterwunderland
00:08:04.009                             : Tag 02 Angriff auf Santa Claus
00:10:35.005                             : Tag 03 Sabotage
00:15:50.988                             : Tag 04 Ein Sack voller Geheimnisse
00:22:22.224                             : Tag 05 36 x Elf
00:30:05.180                             : Tag 06 Bruder Justus
00:36:42.696                             : Tag 07 Elf gegen drei
00:40:48.959                             : Tag 08 Märchenstunde
00:45:05.395                             : Tag 09 Köder mit Schleife
00:53:48.138                             : Tag 10 Auf frischer Tat
00:59:12.627                             : Tag 11 Kurzfinger
01:03:05.516                             : Tag 12 Der Alligator

But the duration entry gets massive out of sync:

yesterday ("Tag 11"):
Duration                                 : 11 h 36 min

today ("Tag 12"):
Duration                                 : 12 h 48 min

Track 12 is:
Duration                                 : 6 min 10 s

[sandreas]

Thanks for reporting.

Could you please provide the following:

• the exact command you used for the conversion, so that I can try to reproduce the issue
• the version of m4b-tool you used
• the operating system you used (probably I don't need this, but just in case)

Is the title Die drei ??? - Eine schreckliche Bescherung: Angriff auf Santa Claus? In this case there is a copyright and maybe I need to invite you to a special private repository, where you can provide your original files via link only for reproducing the issue in case I cannot reproduce the problem with dummy files I usually use.

[lduesing]

Oh. Sorry.
docker run -it --rm -u $(id -u):$(id -g) -v "$(pwd)":/mnt m4b-tool merge -v --jobs=2 --output-file="output/" --batch-pattern="input/%g/%a/%s/%p - %n/" --batch-pattern="input/%g/%a/%n/" "input/"
in the current git-master on Ubuntu 22.04.1 LTS

Yes, that's ???, and copyrighted, complete nearly 1 GB of flac.