TransientDataAccessResourceException - R2DBC pgdb connection remains in idle in transaction - spring-boot

Question

I have a spring-boot application where using webflux and r2dbc-postgres. I have discovered a strange issue when trying to do some db operations in a flatMap().
Code example:
#Transactional
public Mono<Void> insertDummyFooBars() {
return Flux.fromIterable(IntStream.rangeClosed(1, 260).boxed().collect(Collectors.toList()))
.log()
.flatMap(i -> this.repository.save(FooBar.builder().foo("test-" + i).build()))
.log()
.concatMap(i -> this.repository.findAll())
.then();
}
It seems like flatMap can process max 256 elements in batches. (Queues.SMALL_BUFFER_SIZE default value is 256). So when I tried to run the code above (with 260 elements) I've got an exception - TransientDataAccessResourceException and the following message:
Cannot exchange messages because the request queue limit is exceeded; nested exception is io.r2dbc.postgresql.client.ReactorNettyClient$RequestQueueException
There is no Releasing R2DBC Connection after this exception. The pgdb connection/session remains in idle in transaction state and the app is not able to run properly when pool max size is reached and all of the connections are in idle in transaction state. I think the connection should be released even if an exception happened or not.
If I use concatMap instead of flatMap it works as expected - no exception, connection released! It's also ok with flatMap when the elements are less than or equal to 256.
Is it possible to force pgdb connection closure? What should I do If I have lot of db operations in flatMap like this? Should I replace all of them with concatMap? Is there a global solution for this?
Versions:
Postgres: 12.6, Spring-boot: 2.7.6
Demo project
LOG:
2022-12-08 16:32:13.092 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.Iterable.1 : | onNext(256)
2022-12-08 16:32:13.092 DEBUG 17932 --- [actor-tcp-nio-1] o.s.r2dbc.core.DefaultDatabaseClient : Executing SQL statement [INSERT INTO foo_bar (foo) VALUES ($1)]
2022-12-08 16:32:13.114 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.FlatMap.2 : onNext(FooBar(id=258, foo=test-1))
2022-12-08 16:32:13.143 DEBUG 17932 --- [actor-tcp-nio-1] o.s.r2dbc.core.DefaultDatabaseClient : Executing SQL statement [SELECT foo_bar.* FROM foo_bar]
2022-12-08 16:32:13.143 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.Iterable.1 : | request(1)
2022-12-08 16:32:13.143 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.Iterable.1 : | onNext(257)
2022-12-08 16:32:13.144 DEBUG 17932 --- [actor-tcp-nio-1] o.s.r2dbc.core.DefaultDatabaseClient : Executing SQL statement [INSERT INTO foo_bar (foo) VALUES ($1)]
2022-12-08 16:32:13.149 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.Iterable.1 : | onComplete()
2022-12-08 16:32:13.149 INFO 17932 --- [actor-tcp-nio-1] reactor.Flux.Iterable.1 : | cancel()
2022-12-08 16:32:13.160 ERROR 17932 --- [actor-tcp-nio-1] reactor.Flux.FlatMap.2 : onError(org.springframework.dao.TransientDataAccessResourceException: executeMany; SQL [INSERT INTO foo_bar (foo) VALUES ($1)]; Cannot exchange messages because the request queue limit is exceeded; nested exception is io.r2dbc.postgresql.client.ReactorNettyClient$RequestQueueException: [08006] Cannot exchange messages because the request queue limit is exceeded)
2022-12-08 16:32:13.167 ERROR 17932 --- [actor-tcp-nio-1] reactor.Flux.FlatMap.2 :
org.springframework.dao.TransientDataAccessResourceException: executeMany; SQL [INSERT INTO foo_bar (foo) VALUES ($1)]; Cannot exchange messages because the request queue limit is exceeded; nested exception is io.r2dbc.postgresql.client.ReactorNettyClient$RequestQueueException: [08006] Cannot exchange messages because the request queue limit is exceeded
at org.springframework.r2dbc.connection.ConnectionFactoryUtils.convertR2dbcException(ConnectionFactoryUtils.java:215) ~[spring-r2dbc-5.3.24.jar:5.3.24]
at org.springframework.r2dbc.core.DefaultDatabaseClient.lambda$inConnectionMany$8(DefaultDatabaseClient.java:147) ~[spring-r2dbc-5.3.24.jar:5.3.24]
at reactor.core.publisher.Flux.lambda$onErrorMap$29(Flux.java:7105) ~[reactor-core-3.4.25.jar:3.4.25]
at reactor.core.publisher.Flux.lambda$onErrorResume$30(Flux.java:7158) ~[reactor-core-3.4.25.jar:3.4.25]
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:94) ~[reactor-core-3.4.25.jar:3.4.25]
I have tried to change the Queues.SMALL_BUFFER_SIZE, and also tried to add a concurrency value to the flatmap. It works when I reduced the value to 255 but I think it is not a good solution.