Labour Hours vs Overhead Hours

When recording labour transactions what causes there to be a difference between the Labour Hours and the overhead hours for a specific Operation?

For most of our resource groups the actual labour hours and overhead hours shows as the same, but for 2 resource groups the hours are different - what causes this?

Many Thanks

Are you talking about the actual or estimate?

Actual

@paul_luvaglia
Could you check the burden hours setup for the resource group

All Resource Groups have Split Burden (our version its Split O/head)
All except two resource groups are posting labour = overhead hours.

Please check the Crew size or no resources. Basically it happens when multiple employee reports hours against an operation.