dovecot deliver does not use same user-id for auto-indexing in FTS as it does for IMAP searches

Using dovecot 2.3.7.2 with solr 8.11.2 when I do:

doveadm search -u user mailbox INBOX subject "something"

I get multiple mail ID's.

When I start a manual IMAP session and login as that user, select INBOX, and try the command:

. search subject "something"

It returns zero mail ID's; this is consistent across all searches using IMAP - no results returned, no matter what I search for in IMAP.

Further investigation shows that the SOLR search via doveadm is using just the 'username', whereas the IMAP search is using the full email address (and finding nothing).

Worse, with auto-update of the FTS turned on, the user-id used when updating as mail arrives is the domain-less user-id.

Is there a way to change this behaviour, or at least make it consistent?

The dovecot -n command returns:

# 2.3.7.2 (3c910f64b): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.5.7.2 ()
# OS: Linux 5.4.0-125-generic x86_64 Ubuntu 20.04.5 LTS
# Hostname: WITHELD
mail_location = maildir:~/Mail
mail_plugins = " fts fts_solr virtual"
mail_privileged_group = mail
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext
namespace {
  location = virtual:~/Mail/virtual
  prefix = virtual.
  separator = .
}
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  mailbox virtual.All {
    comment = All my messages
    special_use = \All
  }
  prefix =
}
passdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
passdb {
  driver = pam
}
plugin {
  fts = solr
  fts_autoindex = yes
  fts_enforced = yes
  fts_solr = url=http://localhost:8983/solr/dovecot/
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
protocols = " imap lmtp sieve pop3 sieve"
service imap {
  vsz_limit = 4 G
}
service index-worker {
  vsz_limit = 2 G
}
service indexer-worker {
  vsz_limit = 2 G
}
service lmtp {
  inet_listener lmtp {
    address = 127.0.0.1
    port = 24
  }
}
ssl_cert = </etc/letsencrypt/live/WITHELD/fullchain.pem
ssl_client_ca_dir = /etc/ssl/certs
ssl_dh = # hidden, use -P to show it
ssl_key = # hidden, use -P to show it
userdb {
  args = /etc/dovecot/dovecot-sql.conf.ext
  driver = sql
}
userdb {
  driver = passwd
}
protocol lmtp {
  mail_plugins = " fts fts_solr virtual sieve"
  postmaster_address = WITHELD
}
protocol lda {
  mail_plugins = " fts fts_solr virtual sieve"
}
protocol imap {
  mail_max_userip_connections = 40
}