This occurs when the leave taken hours exceed the entitlement hours. The Entitled Hours on the Leave Summary and Liability report are the difference between the entitlement hours and the leave taken hours on the employee record. If the entitled hours are negative, the leave entitlement will appear in the Pre 93 line, and the pro-rata hours will appear on the Post 93 line item.
To avoid this issue, untick Separate Pre and Post values on the Options tab when you run the Leave Summary and Liability report, and one line per employee will appear for Long Service Leave hours.