Tested this on CVHP for hspl company

Steps:-
1] Considered an existing enrollment effective from 03/01/2015 to NULL for an EE for Delta Dental PPO plan with Billed rate as 9.5

2] Generated an Invoice for May 2016. On this generated report searched for the above EE and observed the below :-

For the billing details sections blank data is displayed for the Delta Dental Enrollment. For the adjustment details section the data is displayed properly with cost as 9.5 for every month till April 2016. This is as per expectation.

Now I changed the billed rate for dental rate as 3.5. Recalculated the rate. Again now I generate the Invoice for the month June 2016. Here when I search for the EE the billing details section shows blank record which is not as expected. Also the adjustment details section displays records with negative costs i.e -9.5 for all the months till May 2016 but does not display records with 3.5 for all the months till May 2016.

Also explained scenario to Prasanna.