When a parameter that is used in the selection formula (record, group or saved data) is changed from non-optional to optional, the clause "not HasValue() or" is not appended to the front of the condition.
The issue has been identified and tracked under ID ADAPT00865055.
This issue is fixed in the Crystal Reports 2008 edition released with BusinessObjects Enterprise XI Release 3.
CR2008 CR 2008 XIR3 XI R3 TITAN RN , 4385490 , KBA , BI-RA-CR , Crystal Reports designer or BusinessViews Manager , Bug Filed
Crystal Reports 2008 V0