importer stuck when the ledger sequence is not contiguous

[FredericHeem]

In the case where the ledger sequence in not contiguous, the import process is stuck:

stellar=# select ledgerseq from ledgerheaders;
 ledgerseq 
-----------
         1
         2
         3
         4
         5
         6
         7
         8
         9
        18
        19

horizon imported log:

StellarCore::LedgerHeader Load (0.4ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]
  History::Ledger Load (0.7ms)  SELECT  "history_ledgers".* FROM "history_ledgers"  ORDER BY "history_ledgers"."sequence" DESC LIMIT 1
  StellarCore::LedgerHeader Load (0.4ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]
  History::Ledger Load (0.6ms)  SELECT  "history_ledgers".* FROM "history_ledgers"  ORDER BY "history_ledgers"."sequence" DESC LIMIT 1
  StellarCore::LedgerHeader Load (0.4ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]
  History::Ledger Load (0.8ms)  SELECT  "history_ledgers".* FROM "history_ledgers"  ORDER BY "history_ledgers"."sequence" DESC LIMIT 1
  StellarCore::LedgerHeader Load (0.4ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]
  History::Ledger Load (0.8ms)  SELECT  "history_ledgers".* FROM "history_ledgers"  ORDER BY "history_ledgers"."sequence" DESC LIMIT 1
  StellarCore::LedgerHeader Load (0.5ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]
  History::Ledger Load (0.8ms)  SELECT  "history_ledgers".* FROM "history_ledgers"  ORDER BY "history_ledgers"."sequence" DESC LIMIT 1
  StellarCore::LedgerHeader Load (0.4ms)  SELECT  "ledgerheaders".* FROM "ledgerheaders" WHERE "ledgerheaders"."ledgerseq" = $1  ORDER BY "ledgerheaders"."ledgerhash" ASC LIMIT 1  [["ledgerseq", 10]]

What's your thought about this behavior ? I am still wondering how the stellar-core ended up into this state of non contiguous ledger sequence. BTW, the whole environment sits all locally with a single node with the latest code. Cheers.