If you look at the original email:
https://lore.kernel.org/linux-ide/20240614122344.1577261-2-cassel@kernel.org/T/#u
and search for 'From the AHCI' you will see that the '>' character is not in the commit log,
so it appears that b4 is incorrectly adding a character that was not part of the commit log of the original email.
$ b4 --version 0.13.0
$ b4 shazam https://lore.kernel.org/linux-ide/20240614122344.1577261-2-cassel@kernel.org/T/#u
$ git show | grep From
If you look at the original email: https://lore.kernel.org/linux-ide/20240614122344.1577261-2-cassel@kernel.org/T/#u and search for 'From the AHCI' you will see that the '>' character is not in the commit log, so it appears that b4 is incorrectly adding a character that was not part of the commit log of the original email.