actual cost split using KSS2 transaction

Hi We recently implemented SAP and we did first month end close and as part CO closing we perform the actual cost splitting using transaction KSS2. The splitting was done correctly, however the actual cost line items by cost center is not equal to the payroll posting we have performed.

for example cost center 1 we have actual payroll postings 60000 and the cost split amount is 58500. When I check cost elements from KSS2 I noticed that the payroll posting (debit lines 60000) and over head postings (credit lines 1500) and the sum 58500 is splitted by activity type labour.

Any response will be appreciated.