dynamic update refused shortly after zone was thawed

The rndc system test failed in system:gcc:buster:amd64 in job#3653879:

2023-09-13 04:19:50 INFO:rndc     I:rndc_tmp_vgoajfpy:checking zone now writable (5)
2023-09-13 04:19:51 INFO:rndc     I:rndc_tmp_vgoajfpy:failed
2023-09-13 04:19:51 INFO:rndc     I:rndc_tmp_vgoajfpy:rndc sync
2023-09-13 04:19:51 INFO:rndc     I:rndc_tmp_vgoajfpy:checking zone was dumped (6)
2023-09-13 04:20:01 INFO:rndc     I:rndc_tmp_vgoajfpy:failed

The test first issues an rndc freeze command. Afterwards, rndc thaw is called and then a dynamic zone update is performed. According to ns2/named.run, the sequence of events seems correct. However, the dynamic update is refused and the message indicates the zone was still frozen - which happens after the zone has been reported as thawed:

13-Sep-2023 04:19:50.883 received control channel command 'freeze'
13-Sep-2023 04:19:50.887 freezing zone 'nil/IN': success
13-Sep-2023 04:19:50.887 freezing all zones: success
13-Sep-2023 04:19:50.959 received control channel command 'thaw'
13-Sep-2023 04:19:50.959 thawing zone 'nil/IN': success
13-Sep-2023 04:19:50.959 thawing all zones: success
13-Sep-2023 04:19:50.959 freeing control connection
13-Sep-2023 04:19:50.987 clientmgr @0x7f01f8e00280 attach: 2
13-Sep-2023 04:19:50.987 query client=0x7f01e3441168 thread=0x7f01fa3fc700(<unknown-query>): query_reset
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 (no-peer): allocate new client
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541: UDP request
13-Sep-2023 04:19:50.987 received client packet from 10.53.0.1#58541
;; ->>HEADER<<- opcode: UPDATE, status: NOERROR, id:  53284
;; flags:; ZONE: 1, PREREQ: 0, UPDATE: 1, ADDITIONAL: 1
;; ZONE SECTION:
;nil.				IN	SOA

;; UPDATE SECTION:
;text3.nil.		600	IN	TXT	"addition 3"

;; TSIG PSEUDOSECTION:
;local-ddns.		0	ANY	TSIG	hmac-sha256. 1694578790 300 32 (
;						nQa3VUoXEpPfl0juk40ALpyujNrs
;						XztiFcMzLq8/9/0= ) 53284 NOERROR 0 


13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541: using view '_default'
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541: request has valid signature: local-ddns
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541/key local-ddns: recursion not available (recursion not enabled for view)
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541/key local-ddns: updating zone 'nil/IN': update failed: dynamic update temporarily disabled because the zone is frozen.  Use 'rndc thaw' to re-enable updates. (REFUSED)
13-Sep-2023 04:19:50.987 client @0x7f01e3441168 10.53.0.1#58541/key local-ddns: reset client