I am encountering the problem as described in the subject of this email.

I hope you could enlighten me again about this issue.

Some brief context:
I am trying to build a kind of swiper/swoop for searching documents.
I have tried to use Ivy/Vertico (see
https://github.com/minad/consult/issues/625),
but I think they are not well suited/too heavy for this. So, I concluded
that,
unfortunately, I have to 'reinvent the wheel'.

Anyway, to reproduce the issue starting from emacs -q,
please load the attached file and do `M-x baleen` (the file is large because
it includes the text of `An Introduction to Programming in Emacs Lisp`).
Then type 'ho' and optionally continue typing to narrow down the results.
Press RET to finish (I am just starting development, so never mind further
'testing' the current functionality. Although of course, suggestions for
improvements are welcome).
As you will find, hopefully, things seem to work fine.
Page numbers are nicely displayed in the margins.

Now, do `M-x baleen2`. This time, the data consists of the contents of the
the book `An Introduction to Programming in Emacs Lisp.' Now type e.g.
'emacs' to narrow down the results. The page numbers are not displayed
in the margins, to show that things still work fine.

NOTE the next step should (well, should not of course) make Emacs hang:

Now just uncomment the line
  ;; (set-window-margins nil 4)
in the function `baleen2` and repeat the last step (`M-x baleen2`).
Again, try to type 'emacs'. Unfortunately, Emacs more or less hangs.

I have no idea why suddenly Emacs hangs. I was wondering if any of
you could explain this behavior, and hopefully suggest how to
prevent it.
(Of course, if there is no other solution, then I could just display the
page numbers in the buffer text).

I also have a second question, but I will send it in another mail (with its
own subject).