Nested 'break'

I'm having trouble using nested break. (The code in question is generated,
so I understand this is nothing like idiomatic Scheme!)

Here's a minimum failing example with Guile 3.0.11:

(let ((i 0) (j 0))
  (while #t
    (set! i (+ i 1))
    (if (eqv? i 5) (break))
    (display i)
    (display "\n")
    (set! j 0)
    (while #t
      (set! j (+ j 1))
      (if (eqv? j 5) (break))
      (display j))
    (display "\n")))

This is supposed to print

1
1234
2
1234
3
1234
4
1234

But instead I get:

1
1234
2
1234Backtrace:
In ice-9/boot-9.scm:
  1752:10  7 (with-exception-handler _ _ #:unwind? _ # _)
In unknown file:
           6 (apply-smob/0 #<thunk 784aa970f300>)
In ice-9/boot-9.scm:
    724:2  5 (call-with-prompt ("prompt") #<procedure 784aa971c280 =E2=80=
=A6> =E2=80=A6)
In ice-9/eval.scm:
    619:8  4 (_ #(#(#<directory (guile-user) 784aa9712c80>)))
In ice-9/boot-9.scm:
   2836:4  3 (save-module-excursion #<procedure 784aa9704300 at ice-=E2=80=
=A6>)
  4388:12  2 (_)
In /home/rrt/Software/ursa/./loops-for:
    10:21  1 (_)
In unknown file:
           0 (_ #<procedure abort-to-prompt (_ . _)>)

ERROR: In procedure abort: Abort to unknown prompt

I am not very experienced in Scheme, but my bes understanding of this is
that something has gone wrong with the inner "break".

The source position 10:21 is indeed immediately after "(eqv? j 5)"

As far as I can tell from the Guile manual, this nested use of break should
work fine, so I assume I am doing something basic wrong, but I can't see
what!

--=20
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