2 records loaded (Upsert), 4 reported as processed and 2 failed

[Stepan007]

I'm trying to load two records of c2g__codaGeneralLedgerAccount__c object and even though they are loaded successfully the issue is reported, moreover it says 4 records processed:
"WARNING: [15:39:55.604] [WARN] [Batch# REST:Insert] {c2g__codaGeneralLedgerAccount__c} Completed with issues. 4 records processed, 2 records failed."

What is going on? I'm running Upsert operation but the behaviour is the same for Insert.

target/c2g__codaGeneralLedgerAccount__c_insert_target.csv:
c2g__AllowRevaluation__c,c2g__BalanceSheet1__c,c2g__BalanceSheet2__c,c2g__BalanceSheet3__c,c2g__ReportingCode__c,c2g__TrialBalance1__c,c2g__TrialBalance2__c,c2g__TrialBalance3__c,c2g__TrialBalance4__c,c2g__Type__c,Dimension_1_Required__c,Dimension_2_Required__c,Dimension_3_Required__c,Dimension_4_Required__c,Errors,Id,Name
true,,,,1210,Balance Sheet,1.Current Assets,3.Accounts Receivable,,Balance Sheet,false,false,false,false,,a9LS8000000FxuFMAS,1210 - Accounts Receivables
true,,,,1710,Balance Sheet,3.Current Liabilities,2.Accounts Payable,,Balance Sheet,false,false,false,false,,a9LS8000000FxuGMAS,1710 - Accounts Payable
false,,,,,,,,,,false,false,false,false,Required fields are missing: [c2g__ReportingCode__c],,'1210 - Acconts Recevables'
false,,,,,,,,,,false,false,false,false,Required fields are missing: [c2g__ReportingCode__c],,'1710 - Accounts Payable'

[Stepan007]

It seems for some reason SFDMU decides to create additional two records with some fake IDs and the rest of columns set to blank...why? It doesn't happen for other objects...

c2g__AllowRevaluation__c,c2g__BalanceSheet1__c,c2g__BalanceSheet2__c,c2g__BalanceSheet3__c,c2g__ReportingCode__c,c2g__TrialBalance1__c,c2g__TrialBalance2__c,c2g__TrialBalance3__c,c2g__TrialBalance4__c,c2g__Type__c,Dimension_1_Required__c,Dimension_2_Required__c,Dimension_3_Required__c,Dimension_4_Required__c,Id,Name
true,,,,1210,Balance Sheet,1.Current Assets,3.Accounts Receivable,,Balance Sheet,false,false,false,false,a9LS8000000FxvrMAC,1210 - Accounts Receivables
true,,,,1710,Balance Sheet,3.Current Liabilities,2.Accounts Payable,,Balance Sheet,false,false,false,false,a9LS8000000FxvsMAC,1710 - Accounts Payable
,,,,,,,,,,,,,,ID0000000000000001,'1210 - Acconts Recevables'
,,,,,,,,,,,,,,ID0000000000000002,'1710 - Accounts Payable

[Stepan007]

Just to add to the above, SFDMU creates those additional 2 records already in source. Any explanation for that?