Sending a patch with multiline [] comment in trailers

[martinetd]

I've tried to use b4 to send a stable patch just now, but it's moving my backport comment out of the trailers.

$ b4 prep -n test
Created new branch b4/test
Created the default cover letter, you can edit with --edit-cover.
$ git commit --allow-empty -m 'test
> 
> body
>
> Signed-off-by: foo
> [some comment
> on two lines]
> Signed-off-by: bar'
[b4/test 1d42d1b58227] test
$ b4 send -o tt
Converted the branch to 1 messages
Will write out messages into tt
  0001-test.eml
---
DRYRUN: Would have sent 1 messages
$ cat tt/0001-test.eml
[...]
Date: Tue, 30 Jun 2026 17:18:57 +0900
Subject: [PATCH] test
[...]

body

[some comment
on two lines]

Signed-off-by: foo
Signed-off-by: bar

If the comment is on a single line then it works fine, but while I think such comment should be kept short I often see multi-line ones so I think it's legit?
Or is it not supported on purpose?

(happens anywhere from somewhere after v0.12.0 to current master; didn't try earlier versions)

Thanks!