Hi,
Once IT0581 is maintained, dynamic action leads to IT0008 and adds respective wage type.
However, when a new accommodation type is maintained in IT0581 split, dynamic action tries to insert the HRA wage type in IT0008 even if HRA wage type was available in IT0008.
Ideally, SAP should have deleted the old wage type and insert the new one. But, SAP doesn't delete any wage type / amount in IT0008. So, one has to delete it manually.
If you have any program that maintains IT0581 for large number of employees, your ABAPer needs to write logic for deletion of older Wage type. Or writing user exit will also help.
Only one WT is required for Income Tax calculations.
Hope this helps you.
Regards,
Ajinkya