bug#11261: 24.1.50; cursor doesn't move in a long line

[Katsumi Yamaoka]

Hi,

When I view an html source, of which lines are very long, I meet
with a symptom that C-f, C-b, and so forth don't move the cursor.
One discovered yesterday that it happens only when the header line
exists in a buffer (we use emacs-w3m that ises the header line for
the tab browsing).  Here's a recipe to reproduce this with Emacs -Q:

(let ((fox "The quick brown fox jumps over the lazy dog."))
  (pop-to-buffer "*testing*")
  (erase-buffer)
  (setq header-line-format fox)
  (dotimes (var 1000)
    (insert fox "  "))
  (goto-char (point-min))
  (search-forward "fox" nil t 500))

Could this be fixed?

Thanks in advance.
Regards,