The value of the Deparment attribute is not deleted by FIM portal

I use WSS3.0 as portal of FIM2010.
When I made FIM-MA and exported an account to portal of the FIM from AD of the base, malfunction happened.
I stay once without the value of Department attribute and the Company attribute being deleted on the FIM portal when I synchronize with Department of the account that synchronized after deletion in the information of the Company attribute again on AD.
Is this movement specifications? In addition, please tell me if there is a method to let FIM portal reflect the information that deleted the value on AD.