Problem when I use alias with deferencing option

Hi, I have a problem when I use the alias. I have an OpenLdap with 450.000 entries and 450.000 alias. When I make a search using the deferencing I obtain a wrong result. For example: - if I search in the alias tree uid=xxxx I obtain zero entry but I have the alias and I have the phisical entry - if I search in the alias tree ou=xxxx I obtain a number of entries that is different from same search performed on the phisical tree

This happens only when I use the deferencing option.

Why?

I find in Internet that: "If you have a thousand or more alias objects, avoid alias dereferencing in the search" .... this means I could get wrong results using alias?

Thanks in advance Regards Paola