It could be that Qlikview sees the values as the same. For example, if a data field loads 003 in the first line and 03 in a later line, QV will interpret them both as the number 3, and give them the default format of '000' (from the first line).
If you post an example file, you will get more specific and accurate help.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein