Query Output not proper

Hi,

We have query in which below part is in Where clause

nvl(fdi.end_time, sysdate) = nvl((SELECT max(end_time) from fsi_data_identity fdid WHERE fdid.description = fdi.description),sysdate)

Query doesn't returns incomplete set of records

Expected set of records were 15

Record count retrieved were only 5

But when we revesed the Left hand side with Right Hand side.

nvl((SELECT max(end_time) from fsi_data_identity fdid WHERE fdid.description = fdi.description),sysdate) =nvl(fdi.end_time, sysdate) 

It gave proper record count has 15.

It is happening at customer place but such issues we could not replicate at our dev setup.