AD search weirdness

[JJonas]

Background

We have a students OU and inside this OU are other OU's for the year the student would have started at our school (05,06,07,08,09) Inside these OU's are the student accounts so a student called Fred Bloggs who started in 2007 will be found in the 07 OU with the user name 07BloggsF

The problem

If I go to the students OU and search for Smith it finds all the Smiths in the 05,06 and 07 OU's but will not bring up the Smiths in the 08 or 09 OU's. To find those you have to search for 08Smith or 09Smith.

Why is it doing this? and how do I fix it?