There is no mode binding (`C-h k C-b' returns `backward-char'). I don't know
how to read this (result of showing the keymap in `describe-text-properties'
buffer; at step 1:

(keymap keymap
        (3 keymap
           (5 . magit-diff-edit-hunk-commit)
           (20 . magit-diff-trace-definition))
        (67 . magit-commit-add-log)
        (38 . magit-do-async-shell-command)
        (117 . magit-unstage)
        (115 . magit-stage)
        (97 . magit-apply)
        (remap keymap
               (magit-revert-no-commit . magit-reverse)
               (magit-delete-thing . magit-discard)
               (magit-visit-thing . magit-diff-visit-file))
        (24 keymap
            (97 . magit-add-change-log-entry)
            (53 keymap
                (return . magit-diff-visit-file-other-frame))
            (52 keymap
                (97 . magit-add-change-log-entry-other-window)
                (return . magit-diff-visit-file-other-window)))
        (C-return . magit-diff-visit-worktree-file)
        (10 . magit-diff-visit-worktree-file))

At step 2:

(keymap
 (3 keymap
    (94 keymap
        (108 . magit-smerge-keep-lower)
        (98 . magit-smerge-keep-base)
        (117 . magit-smerge-keep-upper)
        (13 . magit-smerge-keep-current)))
 keymap
 (3 keymap
    (5 . magit-diff-edit-hunk-commit)
    (20 . magit-diff-trace-definition))
 (67 . magit-commit-add-log)
 (38 . magit-do-async-shell-command)
 (117 . magit-unstage)
 (115 . magit-stage)
 (97 . magit-apply)
 (remap keymap
        (magit-revert-no-commit . magit-reverse)
        (magit-delete-thing . magit-discard)
        (magit-visit-thing . magit-diff-visit-file))
 (24 keymap
     (97 . magit-add-change-log-entry)
     (53 keymap
         (return . magit-diff-visit-file-other-frame))
     (52 keymap
         (97 . magit-add-change-log-entry-other-window)
         (return . magit-diff-visit-file-other-window)))
 (C-return . magit-diff-visit-worktree-file)

Paul
 (10 . magit-diff-visit-worktree-file))

On Sat, 27 Aug 2022 at 18:56, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Paul Pogonyshev <pogonyshev@gmail.com>
> > Date: Sat, 27 Aug 2022 18:32:15 +0200
> > Cc: Gerd Möllmann <gerd.moellmann@gmail.com>,
> >       57433@debbugs.gnu.org
> >
> > > Now, I put the point at the beginning of the third line ([^] is the
> point):
> >
> > Text content at position 32867:
> >
> > There is an overlay here:
> >  From 32867 to 32901
> >   evaporate            t
> >   font-lock-face       magit-diff-file-heading-highlight
> >
> > There are text properties here:
> >   font-lock-face       magit-diff-file-heading
> >   keymap               [Show]
> >   magit-section        [Show]
>
> Maybe the 'keymap' part?  Could it be that C-b has a binding in that
> keymap?
>