I faced a bug from days, it takes two days to discover it even though it is a smple thing, but I took that time because I thought logically and the bug is un-logic.
The bug was I have a service that returns a resultset from table in the database and I loop over that resultset, and in the loop I call the function <$getValueForSpecifiedUser(SomeUserName,"dFullName")$> to return the full name of the user in the resultset. I made it and it was working fine for days, then while we prepare to deliver our implementation to the customer, we found the resultset was not displayed correctly just few records is displayed, when you refresh the page multi-times you will got the rest of the records displayed completely (I don't know how this happened).
After removing the function the problem solved. At the end I want to say you should be careful when you deal with resultsets.